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Science of Sintering 50 (2018) 39-50
________________________________________________________________________
_____________________________
) Corresponding author jelenavujancevicitnsanuacrs
doi httpsdoiorg102298SOS1801039V
UDK 546824 622785
Structure and photocatalytic properties of sintered TiO2
nanotube arrays Jelena Vujančević
1) Anđelika Bjelajac
2 Jovana Ćirković
3 Vera
Pavlović4 Endre Horvath
5 Laacuteszloacute Forroacute
5 Branislav Vlahović
67 Miodrag
Mitrić8 Đorđe Janaćković
9 Vladimir Pavlović
1
1Institute of Technical Science of SASA Knez Mihailova 35IV 11000 Belgrade
Serbia 2University of Belgrade Innovation Center of the Faculty of Technology and
Metallurgy Karnegijeva 4 11120 Belgrade Serbia 3University of Belgrade Institute for Multidisciplinary Research Kneza Višeslava 1
11030 Belgrade Serbia 4University of Belgrade Faculty of Mechanical Engineering Kraljice Marije 16
11120 Belgrade 35 Serbia 5Eacutecole Polytechnique Feacutedeacuterale de Lausanne Laboratory of Physics of Complex
Matter (LPMC) 1015 Lausanne Switzerland 6North Carolina Central University Department of Physics 1801 Fayetteville St
Durham North Carolina 27707 USA 7NASA University Research Center for Aerospace Device Research and Education
and NSF Centre of Research Excellence in Science and Technology Computational
Center for Fundamental and Applied Science and Education North Carolina USA 8University of Belgrade Vinča Institute of Nuclear Sciences POBox 522 1101
Belgrade Serbia 9University of Belgrade Faculty of Technology and Metallurgy Karnegijeva 4 11000
Belgrade Serbia
Abstract
One-dimensional (1D) TiO2 nanotubes perpendicular to the substrate were obtained
by electrochemical oxidation of titanium foil in an acid electrolyte In order to alter the
crystallinity and the morphology of films the as-anodized amorphous TiO2 nanotube films
were sintered at elevated temperatures The evolution of the morphology was visualized via
scanning electron microscopy (SEM) while the crystalline structure was investigated by X-
ray diffraction (XRD) and Raman spectroscopy The chemical composition was studied by X-
ray photoelectron spectroscopy (XPS) The effects of crystallinity and morphology of TiO2
nanotube (NTs) films on photocatalytic degradation of methyl orange (MO) in an aqueous
solution under UV light irradiation were also investigated The TiO2 nanotubes sintered at
650 degC for 30 min had the highest degree of crystallinity and exhibited the best photocatalytic
activity among the studied TiO2 nanotube films
Keywords Titanium dioxide Anodization Sintering Crystal phase Photocatalysis
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J Vujančević et al Science of Sintering 50 (2018) 39-50
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1 Introduction
Processes for sustainable environmental protection such as wastewater treatment air
purification and decomposition of undesirable compounds have become a great demand in
modern society Photocatalyst has been introduced with the aim of developing clean chemical
processes and environmentally friendly materials that will degrade harmful pollutants into
non-toxic substances
Photocatalysts are semiconductors that use the energy of light to facilitate the decay
of organic and inorganic pollutants Among the variety of semiconductors such as TiO2 ZnO
[1] ZrO [2] ZnS [3] MoS2 [4] titanium dioxide has become the most commonly used photo-
induced catalyst due to its strong oxidizing capacity [5] chemical stability nontoxicity and
photocorrosion resistance
Many factors influence the photocatalytic performance of TiO2 eg structural
dimensionality size specific surface area pore structure and crystalline phase [6] A high
specific surface area and a unidirectional channel for charge carrier transport can be achieved
by synthesizing one-dimensional nanoarrays This provides a faster electron transport
reducing carrier recombination and improving photocatalytic activity [6]
Along with dimensionality crystal structure plays an important role in the
photocatalytic performance TiO2 has three main crystalline structures anatase rutile and
brookite Anatase and rutile are more efficient in photocatalysis Rutile has a lower band gap
(30 eV) than anatase (32 eV) and it is expected to show better photocatalytic activity
According to previous studies [7-9] rutile turned out to be less efficient than anatase in the
degradation of a large number of organic molecules Sun et al [10] showed that pure anatase
TiO2 nanotubes annealed at 450 degC exhibited the highest photoconversion efficiency of 449
and the maximum hydrogen production rate of 122 μmol(hcm2) Oh et al [11]
demonstrated that the anatase type TiO2 nanotubular film annealed at 550 degC had the best
photocatalytic performance in the photodegradation of aniline blue On the other hand there
are publications showing that rutile exhibits a higher photocatalytic activity than anatase in
the decomposition of methylene blue due to its higher crystallinity [12] Furthermore it
seems that compared to pure anatase or rutile mixed-phase TiO2 shows a higher
photocatalytic activity which is directly related to the surface-phase structure and the phase
junction formed between anatase and rutile [13] Yu et al [14] observed the highest
photocatalytic activity and the highest formation rate of hydroxyl radicals and photocurrent in
the nanotubular TiO2 annealed at 600 degC due to its biphasic structure and good
crystallization Therefore there is a need for a more detailed insight into the temperature
transition of TiO2 polymorphs and their influence onto the photocatalytic performance
It has been established that the temperature of the transition from metastable anatase
to stable rutile depends on many factors such as particle size lattice strain morphology
impurities in the lattice [15] In this article the stability of the structure tube geometries and
the crystal phase transformations upon sintering were investigated The effect of these
parameters on the photocatalytic activity of TiO2 nanotube films was also determined
2 Experimental procedure
Commercial titanium foils (1 times 25 cm2 025 mm thick 997 Aldrich) were
cleaned in an ultrasonic bath with acetone ethanol and deionized water successively After
drying the foils were immersed in 127 wt HF and 053 wt CH3COOH containing
electrolyte along with platinum foil that served as a cathode The distance between the
electrodes was 1 cm Anodization was performed at a potential of 15 V for 30 minutes with
continuous stirring of the electrolyte The samples were dried in air and then annealed at 450
600 650 and 700 degC in the air for 30 minutes with a heating rate of 5 degCmin-1
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41
The morphology evolution was studied using scanning electron microscopy (FEI
NanoSEM 630 15keV)
Raman spectra were obtained in the range from 100 to 1100 cm-1 with a Horiba Jobin
Yvon Aramis RamanPL System using a He-Ne laser operating at 6328 nm with the power
of 1 mW on the sample surface All measurements were performed using a grating with 1800
linesmm a 100times microscope objective and the acquisition of 10s5 cycles
The X-ray Diffraction (XRD) patterns were obtained on a Philips PW-1050
diffractometer operated at 40 kV and 30 mA using Ni-filtered Cu K radiation (15419 Aring)
BraggndashBrentano focusing geometry was used with a fixed 1deg divergence and 01deg receiving
slits The patterns were taken in the 20ndash80deg 2 range with the step of 005deg and collection
time of 1 s per step The crystalline sizes were estimated using Scherrerʼs equation [16] D = k
(βcosθ) where D was crystalline size k the Sherrerʼs constant λ the wavelength of X-ray
radiation β the full-width at half-maximum (FWHM) and θ was the diffraction angle
The XPS measurements were conducted on a Kratos Axis Ultra XPS system with
Monochromated Aluminum K-Alpha X-Rays (h = 14866 eV) During the measurement
chamber vacuum was at 25 times 10-8 torrs The X-Ray gun was operated at 15 kW and 10 mA
A charge neutralizer was used to reduce the charging effects from non-conducting surfaces
All survey scans were collected with a Pass Energy of 160 eV and one sweep (or averaging)
All Region scans were made with a Pass Energy of 20 eV and the number of sweeps
(averages) performed was dependent on the measured region All data was calibrated to the
C-C portion of the C1s peak at 2845 eV
The photocatalytic activity of TiO2 nanotube films on titanium foil was investigated
by immersing the samples into 3 ml of aqueous MO solution (concentration of 5 mgL) In
order to the achieve adsorptiondesorption equilibrium the samples were left in solution for 1
h in the dark prior to the photocatalytic test reaction The sample was illuminated by a spot
light source (Hamamatsu LC5) from a distance of 1 cm (light intensity 52 mWcm2) The
decomposition rate of MO as a function of irradiation time was measured by a Varian Cary 50
Scan UV-Vis spectrophotometer In order to determine the intrinsic photolysis of MO (ie the
UV light-induced self-decomposition) the aqueous solution of MO without photocatalysts
was irradiated
3 Results and Discussion
The anodization of Ti foil is a promising approach to fabricating vertically oriented
TiO2 nanotube arrays directly grown on the Ti substrate without a template The sintering
temperature is an important parameter that affects the morphology and crystallinity of
nanotubes Fig 1 (a-j) shows the evolution of the nanotube morphology as a consequence of
sintering temperature change Tab I shows the influence of the annealing temperature on the
average inner diameter (Di) the wall thickness (W) and the tube length (L) obtained using the
image analysis software The porosity was calculated according to the equation [17]
223
21
WDi
WDiWP
Fig 1a and b show well-defined TiO2 nanotubes formed in an aqueous solution of HF
at a potential of 15 V It is evident that the highly ordered nanotube array consists of very
regular tubes with an average inner diameter of 90 nm and a wall thickness of 10 nm The
length of the tubes is 315 nm with rough walls typical of nanotubes grown in an electrolyte
with water [18] After annealing at 450 degC nanotubular arrays retained their structural
integrity with a slight change in the diameters wall thickness and length as it is shown in
Tab I At 600 degC a compact layer appeared at the interface between the TiO2 nanotubes and
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the titanium foil and due to that the length of nanotubes decrease on L = 220 nm With further
increase in temperature the diameters slightly decreased while the length shortened
drastically This can be presumably ascribed to the sintering process that occurs during
crystallization At 700degC nanotubes no longer had a regular shape with recognizable
particles grown from the nanotubes With sintering the porosity lowered (Tab I) due to the
shrinking of the tubes which merged together reducing the spacing between the walls
Tab I Average morphological parameters for as-anodized and sintered TiO2 nanotubes
Samples Di (nm) W (nm) L (nm) P
As-anodized 90 10 314 070
450 oC 75 13 315 060
600 oC 84 13 222 062
650 oC 72 16 152 053
700 oC 105
Fig 1 SEM micrographs of the top and side views of TiO2 nanotubes sintered at different
temperatures (a and b) as-anodized (c and d) 450 degC (e and f) 600 degC (g and h) 650 degC (i
and j) 700 degC
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In order to determine the phase composition and crystallinity of TiO2 nanotube arrays
at different sintering temperatures the XRD diffractograms and Raman spectra were studied
Fig 2 shows the diffractograms of TiO2 nanotube arrays annealed at a different temperature
The as-anodized TiO2 nanotubes are amorphous due to which only the peaks of the titanium
substrate are present in the diffractogram With annealing TiO2 nanotubes crystallized in two
polymorphous forms anatase and rutile At 450 degC anatase was observed as the main crystal
phase due to the presence of two main anatase peaks at 253deg and 48deg corresponding to the
(101) and (200) planes respectively Also a small amount of the rutile phase appeared at
273deg (110) All other peaks came from the substrate which dominated due to the low
thickness of the film Mor at al [19] reported that in nanotubes on a titanium substrate rutile
appeared at 430 degC while in nanotubes on conductive glass annealed at 500 degC rutile did not
appear This happened due to the growth of rutile crystallites at the interface between the
nanotube bottom and the thermally oxidized Ti substrate [7] With temperature rise to 600 degC
new peaks appeared at 361deg (101) 414deg (111) 44deg (210) 543deg (211) 567deg (220) and 689deg
(301) which corresponded to the rutile phase With further temperature increase up to 650
and 700 degC the intensity of the rutile peaks gradually strengthened while the intensity of
peaks from anatase decreased proving that almost all anatase transformed into rutile A
decrease of the diffraction intensity of the titanium foil was also observed revealing the
crystallization of the support [20] The phase composition and the crystallite size estimated
using Scherrerʼs formula are shown in Tab II The crystal size of anatase and rutile was
growing until the temperature reached 650 degC when it started to drop probably due to the
collapse of the nanotube structure
Fig 2 XRD patterns of the as-anodized and sintered TiO2 nanotubes (A-anatase R-rutile Ti-
titanium)
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Tab II Phase composition and average crystallite size of annealed TiO2 nanotubes
Temperature
of annealing oC
Amount of
anatase phase
Amount of
rutile phase
Crystallite size
for anatase
(101)
Crystallite size
for rutile
(110)
450 997 03 231 54
600 203 797 289 257
650 25 975 262 346
700 06 994 242 273
The temperature-induced anatase and rutile crystal modifications of TiO2 were
tracked using spectroscopy methods The Raman spectrum of the sample annealed at 450 degC
(Fig 3) showed only the Raman peaks characteristic for the crystal modification of anatase at
145 cm-1 (Eg(1) mode) 198 cm-1 (Eg(2) mode) and 395 cm-1 (B1g(1) mode) as well as the
peak at 515 cm-1 that corresponds to the superposition of the A1g and B1g(2) modes and the
peak at 635 cm-1 which comes from the Eg(3) mode [21-23] With an increase in temperature
new peaks started to appear in the Raman spectra along with anatase peaks At 600 degC the
rutile Eg mode at 425 cm-1 occurred besides the anatase modes Further temperature increase
up to 650 degC resulted in more intensive rutile peaks while the intensity of all the major
anatase modes decreased and only the main anatase mode at 145 cm-1 remained clearly
visible
Fig 3 Raman spectra of annealed TiO2 nanotubes (A-anatase R-rutile)
The rutile phase was observed as the dominant one identified by the Eg mode at 446 cm-
1and A1g mode at 609 cm-1 as well as by the broad peak at 242 cm-1 which originated from
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the second-order vibrational mode Eg (SO) and disorder effects [24 25] At 700 degC the main
anatase mode was replaced with the rutile B1g mode at 142 cm-1 indicating that anatase
phase completely disappeared The whole spectrum at this temperature was assigned to the
rutile phase where the four Raman modes were prominent enough (B1g Eg A1g and Eg (SO))
while the mode expected at 826-827 cm-1 was too weak to be observed
An XPS study was further employed in order to investigate how different annealing
temperatures influenced the chemical composition of anodized titanium foil The results are
presented in Fig 4 In pristine TiO2 titanium (Ti 2p) oxygen (O1s) carbon (C1s) nitrogen
(N1s) fluoride (F1s) and lead (4f) XPS peaks were noticed After a heat treatment peaks of
lead fluoride and nitrogen disappeared proving that they were caused by surface
contamination No significant changes were noticed for the samples annealed at 450 and 600
degC relative to pristine samples Since the positions of Ti 2p32 and Ti 2p12 peaks (Fig 5) in
these samples ranged from 45816 to 45837 eV and from 46385 to 46410 eV respectively
it clearly indicated the existence of a Ti4+ state [26 27] Moreover the difference in the
binding energy of Ti 2p32 and Ti 2p12 peaks in all of the annealed samples was in accordance
with the literature data for the mentioned state of titanium Although at higher annealing
temperatures both peaks shifted slightly towards lower binding energies their positions still
remained well above the binding energy of the Ti3+ state [27 28] In the O1s regions of
binding energy the peak at 5296-5297 eV proved O-Ti4+ bonding (Fig 6) [29] It was
possible to assign it to the lattice oxygen in TiO2 On the other hand the shoulder effect that
could be fitted with the peak at 5310 plusmn 02 eV probably originated from surface-adsorbed
oxygen (within the hydroxyl groups at the outermost surface as well as within the adsorbed
water resulting from moisture adsorption in air) [29] The increase in annealing temperature
up to 650 degC caused the reduction of the surface-adsorbed oxygen content The atomic ratio
OlattTi2p provides an insight into the stoichiometry of the structure
Fig 4 XPS survey spectrum for as-anodized TiO2 and sintered TiO2
The results show the substoichiometric structure for the amorphous (as-anodized) sample
(Tab III) which probably indicates the presence of oxygen vacancies in it It can be assumed
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46
that after annealing the filling of oxygen defects proceeded which was assisted by the
crystallization process since annealing was taking place in air
Fig 5 XPS spectrum for Ti 2p peak for as-anodized and sintered TiO2
Tab III XPS results of as-anodized and sintered TiO2
Samples OlattOtot
(area )
OadsOtot
(area )
OlattTi2p
(atomic ratio)
BE(Ti2p12)-BE(Ti2p32)
(eV)
As-
anodized
587 413 16 577
450 oC 799 201 21 573
600 oC 820 180 21 572
650 oC 843 157 21 569
700 oC 815 185 21 572
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
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Fig 6 XPS spectrum for O 1s peak for as-anodized and sintered TiO2
Tab IV Influence of sintering temperature on photocatalytic degradation ndash first-order rate
constant and correlation coefficient
Temperature of
annealing oC
|k| x 10-2
min-1
R2
450 109 096
600 111 098
650 124 094
700 062 090
The influence of the sintering temperature of TiO2 nanotubes on the degradation of the MO
textile dye is shown on Fig 7a A further analysis indicated that the reaction could be
presented as ln(CCo) = ln(AAo) = kt where Co was the initial dye concentration C was the
concentration after irradiation for time t Ao and A were the corresponding absorbance while k
was a rate constant Fig 7b shows the linear curves proving that the degradation of MB by
sintered TiO2 nanotubes follows the pseudo-first order kinetic The first-order constant k and
the correlation coefficient R2 are shown in Tab IV It is evident that an increased annealing
temperature was accompanied by the increase of k up to 700 degC when it began to decrease
gradually The samples sintered at 450 degC and 600 degC had similar morphology parameters but
there was a difference in the crystal structure The reason for a higher kinetic constant for the
sample annealed at 600 degC was probably the presence of the rutile phase The best
photocatalytic activity shows sample annealed at 650 degC due to the optimum ratio of
anataserutile phase The worst photocatalytic performance was exhibited by the sample
annealed at 700 degC and this can be explained by the collapse of the nanotubular morphology
and porosity loss combined with the disappearance of the anatase phase (Fig 2) The
advantages of the mixed anatase-rutile phase could be due to the efficient trapping and
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48
separation of photogenerated charges at the phase junction or the separation of the charges
across different crystallite phases [30]
Fig 7 Effect of sintered TiO2 nanotubes on the photocatalytic MO degradation (a) and
photocatalytic kinetic behavior of the degradation of MO by sintered TiO2 nanotubes (b)
4 Conclusions
In this study a highly ordered TiO2 nanotube array on a Ti substrate was successfully
fabricated using electrochemical anodization It was observed that the morphologies and
crystallinity of the TiO2 nanotube array were greatly influenced by the sintering temperature
It was shown the sample annealed at 450 degC consisted mostly of the anatase phase while 994
of rutile was formed at 700 degC At the temperatures of 600 degC and 650 degC a mixture of
anatase and rutile was observed Different amounts of the polymorph phase strongly
influenced the photodegradation of the MO dye It was established that the TiO2 nanotube
array sintered at 650 degC showed the best photocatalytic activity due to the optimal anatase-to-
rutile ratio With a further increase in temperature up to 700 degC the photocatalytic activity
drastically decreased due to the collapse of the nanotubular structure and the excessive rutile
content As a result of the presented investigation an appropriate tailoring of the ratio of
polymorph phases in TiO2 nanotubes could lead to a more suitable photocatalyst
Acknowledgements
This research was supported by the project OI 172057 and project III 45019 of the
Ministry of Education Science and Technological Development of the Republic of Serbia
and by NSF CREST (HRD-0833184) NASA (NNX09AV07A) and NSF-PREM1523617
awards The work in Lausanne was supported by grants from Switzerland through the Swiss
Contribution (SH7220) E H wants to thank the AIT grant the Zeno-Karl Schindler
foundation and MBR Global Water Initiatives for their support
5 References
1 X Chen Z Wu D Liu and Z Gao Nanoscale Res Lett 12 1 (2017) 143
2 E Bailoacuten-Garciacutea A Elmouwahidi F Carrasco-Mariacuten A F Peacuterez-Cadenas and F J
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
49
Maldonado-Hoacutedar Appl Catal B Environ 217 (2017) 540-550
3 H Zhang X Chen Z Li J Kou T Yu and Z Zou J Phys D Appl Phys 40 21
(2007) 6846-6849
4 M Sabarinathan S Harish J Archana M Navaneethan H Ikeda and Y
Hayakawa RSC Adv 7 40 (2017) 24754-24763
5 M R Hoffmann S T Martin W Choi and D W Bahnemann Chem Rev 95 1
(1995) 69-96
6 K Nakata and A Fujishima J Photochem Photobiol C Photochem Rev 13 3
(2012) 169-189
7 D Fang Z Luo K Huang and D C Lagoudas Appl Surf Sci 257 15 (2011)
6451-6461
8 J M Macak M Zlamal J Krysa and P Schmuki Small 3 2 (2007) 300-304
9 Y Lai L Sun Y Chen H Zhuang C Lin and J W Chin J Electrochem Soc
153 7 (2006) D123
10 Y Sun K Yan G Wang W Guo and T Ma J Phys Chem C 115 26 (2011)
12844-12849
11 H J Oh J H Lee Y J Kim S J Suh J H Lee and C S Chi Appl Catal B
Environ 84 1ndash2 (2008) 142-147
12 N Masahashi Y Mizukoshi S Semboshi and N Ohtsu Appl Catal B Environ
901ndash2 (2009) 255-261
13 J Zhang Q Xu Z Feng M Li and C Li Angew Chemie Int Ed 47 9 (2008)
1766-1769
14 J Yu and B Wang Appl Catal B Environ 94 3ndash4 (2010) 295-302
15 O Carp C L Huisman and A Reller Prog Solid State Chem 32 1ndash2 (2004) 33-
177
16 B D Cullity Elements of x-ray diffraction Reading MA Addison-Wesley
Publishing Company Inc 1978
17 A G Kontos et al Chem Phys Lett 490 1ndash3 (2010) 58-62
18 Z Su and W Zhou J Mater Chem 21 25 (2011) 8955
19 G K Mor O K Varghese M Paulose K Shankar and C a Grimes Sol Energy
Mater Sol Cells 90 14 (2006) 2011-2075
20 Y Li et al Appl Surf Sci 297 (2014) 103-108
21 T Ohsaka F Izumi and Y Fujiki J Raman Spectrosc 7 6 (1978) 321-324
22 W F Zhang Y L He M S Zhang Z Yin and Q Chen J Phys D Appl Phys
33 8 (2000) 912-916
23 H C Choi Y M Jung and S Bin Kim Vib Spectrosc 37 1 (2005) 33-38
24 Y Hara and M Nicol Phys Status Solidi 94 1 (1979) 317-322
25 B Santara P K Giri K Imakita and M Fujii J Phys D Appl Phys47 21 (2014)
215302
26 Z Lou Y Li H Song Z Ye and L Zhu RSC Adv 6 51 (2016) 45343-45348
27 X Zhu J Chen X Yu X Zhu X Gao and K Cen RSC Adv 5 39 (2015) 30416-
30424
28 Y Fu H Du S Zhang and W Huang Mater Sci Eng A 403 1ndash2 (2005) 25-31
29 Z Fan H Guo K Fang and Y Sun RSC Adv 5 31 (2015) 24795-24802
30 Y K Kho A Iwase W Y Teoh L Madler A Kudo and R Amal J Phys Chem
C 114 6 (2010) 2821-2829
Садржај Једнодимензионе наноцеви TiO2 усправно орјентисане на супстрат добијене
су електрохемијском анодизацијом титанијумске фолије у киселом електролиту У
циљу промене кристалне структуре и морфологије филма анодизовани аморфни
J Vujančević et al Science of Sintering 50 (2018) 39-50
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филмови TiO2 синтеровани су на високој температури Морфолошка промена
посматрана је скенирајућом електронском микроскопијом (СЕМ) док је кристална
структура испитивана рендгенском анализом (ХРД) и Раманском спектроскопијом
Хемијски састав је урађен помоћу спектроскопске фотоемисије X-зрака (ХПС) У овом
раду је испитиван утицај кристалне структуре и морфологије нанотубуларног филма
TiO2 на фотокаталитичку деградацију воденог раствора метил оранжа (МО) под
дејством ултраљубичастог зрачења Наноцеви TiO2 синтероване на 650 degC 30 мин
показују најбољу кристалоичност и фотокаталитичку активност у поређењу са
осталим филмовима TiO2
Кључне речи Титанијум диоксид анодизација синтеровање кристална фаза
фотокатализа
copy 2016 Authors Published by the International Institute for the Science of Sintering This
article is an open access article distributed under the terms and conditions of the Creative
Commons mdash Attribution 40 International license
(httpscreativecommonsorglicensesby40)
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
40
1 Introduction
Processes for sustainable environmental protection such as wastewater treatment air
purification and decomposition of undesirable compounds have become a great demand in
modern society Photocatalyst has been introduced with the aim of developing clean chemical
processes and environmentally friendly materials that will degrade harmful pollutants into
non-toxic substances
Photocatalysts are semiconductors that use the energy of light to facilitate the decay
of organic and inorganic pollutants Among the variety of semiconductors such as TiO2 ZnO
[1] ZrO [2] ZnS [3] MoS2 [4] titanium dioxide has become the most commonly used photo-
induced catalyst due to its strong oxidizing capacity [5] chemical stability nontoxicity and
photocorrosion resistance
Many factors influence the photocatalytic performance of TiO2 eg structural
dimensionality size specific surface area pore structure and crystalline phase [6] A high
specific surface area and a unidirectional channel for charge carrier transport can be achieved
by synthesizing one-dimensional nanoarrays This provides a faster electron transport
reducing carrier recombination and improving photocatalytic activity [6]
Along with dimensionality crystal structure plays an important role in the
photocatalytic performance TiO2 has three main crystalline structures anatase rutile and
brookite Anatase and rutile are more efficient in photocatalysis Rutile has a lower band gap
(30 eV) than anatase (32 eV) and it is expected to show better photocatalytic activity
According to previous studies [7-9] rutile turned out to be less efficient than anatase in the
degradation of a large number of organic molecules Sun et al [10] showed that pure anatase
TiO2 nanotubes annealed at 450 degC exhibited the highest photoconversion efficiency of 449
and the maximum hydrogen production rate of 122 μmol(hcm2) Oh et al [11]
demonstrated that the anatase type TiO2 nanotubular film annealed at 550 degC had the best
photocatalytic performance in the photodegradation of aniline blue On the other hand there
are publications showing that rutile exhibits a higher photocatalytic activity than anatase in
the decomposition of methylene blue due to its higher crystallinity [12] Furthermore it
seems that compared to pure anatase or rutile mixed-phase TiO2 shows a higher
photocatalytic activity which is directly related to the surface-phase structure and the phase
junction formed between anatase and rutile [13] Yu et al [14] observed the highest
photocatalytic activity and the highest formation rate of hydroxyl radicals and photocurrent in
the nanotubular TiO2 annealed at 600 degC due to its biphasic structure and good
crystallization Therefore there is a need for a more detailed insight into the temperature
transition of TiO2 polymorphs and their influence onto the photocatalytic performance
It has been established that the temperature of the transition from metastable anatase
to stable rutile depends on many factors such as particle size lattice strain morphology
impurities in the lattice [15] In this article the stability of the structure tube geometries and
the crystal phase transformations upon sintering were investigated The effect of these
parameters on the photocatalytic activity of TiO2 nanotube films was also determined
2 Experimental procedure
Commercial titanium foils (1 times 25 cm2 025 mm thick 997 Aldrich) were
cleaned in an ultrasonic bath with acetone ethanol and deionized water successively After
drying the foils were immersed in 127 wt HF and 053 wt CH3COOH containing
electrolyte along with platinum foil that served as a cathode The distance between the
electrodes was 1 cm Anodization was performed at a potential of 15 V for 30 minutes with
continuous stirring of the electrolyte The samples were dried in air and then annealed at 450
600 650 and 700 degC in the air for 30 minutes with a heating rate of 5 degCmin-1
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
41
The morphology evolution was studied using scanning electron microscopy (FEI
NanoSEM 630 15keV)
Raman spectra were obtained in the range from 100 to 1100 cm-1 with a Horiba Jobin
Yvon Aramis RamanPL System using a He-Ne laser operating at 6328 nm with the power
of 1 mW on the sample surface All measurements were performed using a grating with 1800
linesmm a 100times microscope objective and the acquisition of 10s5 cycles
The X-ray Diffraction (XRD) patterns were obtained on a Philips PW-1050
diffractometer operated at 40 kV and 30 mA using Ni-filtered Cu K radiation (15419 Aring)
BraggndashBrentano focusing geometry was used with a fixed 1deg divergence and 01deg receiving
slits The patterns were taken in the 20ndash80deg 2 range with the step of 005deg and collection
time of 1 s per step The crystalline sizes were estimated using Scherrerʼs equation [16] D = k
(βcosθ) where D was crystalline size k the Sherrerʼs constant λ the wavelength of X-ray
radiation β the full-width at half-maximum (FWHM) and θ was the diffraction angle
The XPS measurements were conducted on a Kratos Axis Ultra XPS system with
Monochromated Aluminum K-Alpha X-Rays (h = 14866 eV) During the measurement
chamber vacuum was at 25 times 10-8 torrs The X-Ray gun was operated at 15 kW and 10 mA
A charge neutralizer was used to reduce the charging effects from non-conducting surfaces
All survey scans were collected with a Pass Energy of 160 eV and one sweep (or averaging)
All Region scans were made with a Pass Energy of 20 eV and the number of sweeps
(averages) performed was dependent on the measured region All data was calibrated to the
C-C portion of the C1s peak at 2845 eV
The photocatalytic activity of TiO2 nanotube films on titanium foil was investigated
by immersing the samples into 3 ml of aqueous MO solution (concentration of 5 mgL) In
order to the achieve adsorptiondesorption equilibrium the samples were left in solution for 1
h in the dark prior to the photocatalytic test reaction The sample was illuminated by a spot
light source (Hamamatsu LC5) from a distance of 1 cm (light intensity 52 mWcm2) The
decomposition rate of MO as a function of irradiation time was measured by a Varian Cary 50
Scan UV-Vis spectrophotometer In order to determine the intrinsic photolysis of MO (ie the
UV light-induced self-decomposition) the aqueous solution of MO without photocatalysts
was irradiated
3 Results and Discussion
The anodization of Ti foil is a promising approach to fabricating vertically oriented
TiO2 nanotube arrays directly grown on the Ti substrate without a template The sintering
temperature is an important parameter that affects the morphology and crystallinity of
nanotubes Fig 1 (a-j) shows the evolution of the nanotube morphology as a consequence of
sintering temperature change Tab I shows the influence of the annealing temperature on the
average inner diameter (Di) the wall thickness (W) and the tube length (L) obtained using the
image analysis software The porosity was calculated according to the equation [17]
223
21
WDi
WDiWP
Fig 1a and b show well-defined TiO2 nanotubes formed in an aqueous solution of HF
at a potential of 15 V It is evident that the highly ordered nanotube array consists of very
regular tubes with an average inner diameter of 90 nm and a wall thickness of 10 nm The
length of the tubes is 315 nm with rough walls typical of nanotubes grown in an electrolyte
with water [18] After annealing at 450 degC nanotubular arrays retained their structural
integrity with a slight change in the diameters wall thickness and length as it is shown in
Tab I At 600 degC a compact layer appeared at the interface between the TiO2 nanotubes and
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
42
the titanium foil and due to that the length of nanotubes decrease on L = 220 nm With further
increase in temperature the diameters slightly decreased while the length shortened
drastically This can be presumably ascribed to the sintering process that occurs during
crystallization At 700degC nanotubes no longer had a regular shape with recognizable
particles grown from the nanotubes With sintering the porosity lowered (Tab I) due to the
shrinking of the tubes which merged together reducing the spacing between the walls
Tab I Average morphological parameters for as-anodized and sintered TiO2 nanotubes
Samples Di (nm) W (nm) L (nm) P
As-anodized 90 10 314 070
450 oC 75 13 315 060
600 oC 84 13 222 062
650 oC 72 16 152 053
700 oC 105
Fig 1 SEM micrographs of the top and side views of TiO2 nanotubes sintered at different
temperatures (a and b) as-anodized (c and d) 450 degC (e and f) 600 degC (g and h) 650 degC (i
and j) 700 degC
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
43
In order to determine the phase composition and crystallinity of TiO2 nanotube arrays
at different sintering temperatures the XRD diffractograms and Raman spectra were studied
Fig 2 shows the diffractograms of TiO2 nanotube arrays annealed at a different temperature
The as-anodized TiO2 nanotubes are amorphous due to which only the peaks of the titanium
substrate are present in the diffractogram With annealing TiO2 nanotubes crystallized in two
polymorphous forms anatase and rutile At 450 degC anatase was observed as the main crystal
phase due to the presence of two main anatase peaks at 253deg and 48deg corresponding to the
(101) and (200) planes respectively Also a small amount of the rutile phase appeared at
273deg (110) All other peaks came from the substrate which dominated due to the low
thickness of the film Mor at al [19] reported that in nanotubes on a titanium substrate rutile
appeared at 430 degC while in nanotubes on conductive glass annealed at 500 degC rutile did not
appear This happened due to the growth of rutile crystallites at the interface between the
nanotube bottom and the thermally oxidized Ti substrate [7] With temperature rise to 600 degC
new peaks appeared at 361deg (101) 414deg (111) 44deg (210) 543deg (211) 567deg (220) and 689deg
(301) which corresponded to the rutile phase With further temperature increase up to 650
and 700 degC the intensity of the rutile peaks gradually strengthened while the intensity of
peaks from anatase decreased proving that almost all anatase transformed into rutile A
decrease of the diffraction intensity of the titanium foil was also observed revealing the
crystallization of the support [20] The phase composition and the crystallite size estimated
using Scherrerʼs formula are shown in Tab II The crystal size of anatase and rutile was
growing until the temperature reached 650 degC when it started to drop probably due to the
collapse of the nanotube structure
Fig 2 XRD patterns of the as-anodized and sintered TiO2 nanotubes (A-anatase R-rutile Ti-
titanium)
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
44
Tab II Phase composition and average crystallite size of annealed TiO2 nanotubes
Temperature
of annealing oC
Amount of
anatase phase
Amount of
rutile phase
Crystallite size
for anatase
(101)
Crystallite size
for rutile
(110)
450 997 03 231 54
600 203 797 289 257
650 25 975 262 346
700 06 994 242 273
The temperature-induced anatase and rutile crystal modifications of TiO2 were
tracked using spectroscopy methods The Raman spectrum of the sample annealed at 450 degC
(Fig 3) showed only the Raman peaks characteristic for the crystal modification of anatase at
145 cm-1 (Eg(1) mode) 198 cm-1 (Eg(2) mode) and 395 cm-1 (B1g(1) mode) as well as the
peak at 515 cm-1 that corresponds to the superposition of the A1g and B1g(2) modes and the
peak at 635 cm-1 which comes from the Eg(3) mode [21-23] With an increase in temperature
new peaks started to appear in the Raman spectra along with anatase peaks At 600 degC the
rutile Eg mode at 425 cm-1 occurred besides the anatase modes Further temperature increase
up to 650 degC resulted in more intensive rutile peaks while the intensity of all the major
anatase modes decreased and only the main anatase mode at 145 cm-1 remained clearly
visible
Fig 3 Raman spectra of annealed TiO2 nanotubes (A-anatase R-rutile)
The rutile phase was observed as the dominant one identified by the Eg mode at 446 cm-
1and A1g mode at 609 cm-1 as well as by the broad peak at 242 cm-1 which originated from
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
45
the second-order vibrational mode Eg (SO) and disorder effects [24 25] At 700 degC the main
anatase mode was replaced with the rutile B1g mode at 142 cm-1 indicating that anatase
phase completely disappeared The whole spectrum at this temperature was assigned to the
rutile phase where the four Raman modes were prominent enough (B1g Eg A1g and Eg (SO))
while the mode expected at 826-827 cm-1 was too weak to be observed
An XPS study was further employed in order to investigate how different annealing
temperatures influenced the chemical composition of anodized titanium foil The results are
presented in Fig 4 In pristine TiO2 titanium (Ti 2p) oxygen (O1s) carbon (C1s) nitrogen
(N1s) fluoride (F1s) and lead (4f) XPS peaks were noticed After a heat treatment peaks of
lead fluoride and nitrogen disappeared proving that they were caused by surface
contamination No significant changes were noticed for the samples annealed at 450 and 600
degC relative to pristine samples Since the positions of Ti 2p32 and Ti 2p12 peaks (Fig 5) in
these samples ranged from 45816 to 45837 eV and from 46385 to 46410 eV respectively
it clearly indicated the existence of a Ti4+ state [26 27] Moreover the difference in the
binding energy of Ti 2p32 and Ti 2p12 peaks in all of the annealed samples was in accordance
with the literature data for the mentioned state of titanium Although at higher annealing
temperatures both peaks shifted slightly towards lower binding energies their positions still
remained well above the binding energy of the Ti3+ state [27 28] In the O1s regions of
binding energy the peak at 5296-5297 eV proved O-Ti4+ bonding (Fig 6) [29] It was
possible to assign it to the lattice oxygen in TiO2 On the other hand the shoulder effect that
could be fitted with the peak at 5310 plusmn 02 eV probably originated from surface-adsorbed
oxygen (within the hydroxyl groups at the outermost surface as well as within the adsorbed
water resulting from moisture adsorption in air) [29] The increase in annealing temperature
up to 650 degC caused the reduction of the surface-adsorbed oxygen content The atomic ratio
OlattTi2p provides an insight into the stoichiometry of the structure
Fig 4 XPS survey spectrum for as-anodized TiO2 and sintered TiO2
The results show the substoichiometric structure for the amorphous (as-anodized) sample
(Tab III) which probably indicates the presence of oxygen vacancies in it It can be assumed
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
46
that after annealing the filling of oxygen defects proceeded which was assisted by the
crystallization process since annealing was taking place in air
Fig 5 XPS spectrum for Ti 2p peak for as-anodized and sintered TiO2
Tab III XPS results of as-anodized and sintered TiO2
Samples OlattOtot
(area )
OadsOtot
(area )
OlattTi2p
(atomic ratio)
BE(Ti2p12)-BE(Ti2p32)
(eV)
As-
anodized
587 413 16 577
450 oC 799 201 21 573
600 oC 820 180 21 572
650 oC 843 157 21 569
700 oC 815 185 21 572
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
47
Fig 6 XPS spectrum for O 1s peak for as-anodized and sintered TiO2
Tab IV Influence of sintering temperature on photocatalytic degradation ndash first-order rate
constant and correlation coefficient
Temperature of
annealing oC
|k| x 10-2
min-1
R2
450 109 096
600 111 098
650 124 094
700 062 090
The influence of the sintering temperature of TiO2 nanotubes on the degradation of the MO
textile dye is shown on Fig 7a A further analysis indicated that the reaction could be
presented as ln(CCo) = ln(AAo) = kt where Co was the initial dye concentration C was the
concentration after irradiation for time t Ao and A were the corresponding absorbance while k
was a rate constant Fig 7b shows the linear curves proving that the degradation of MB by
sintered TiO2 nanotubes follows the pseudo-first order kinetic The first-order constant k and
the correlation coefficient R2 are shown in Tab IV It is evident that an increased annealing
temperature was accompanied by the increase of k up to 700 degC when it began to decrease
gradually The samples sintered at 450 degC and 600 degC had similar morphology parameters but
there was a difference in the crystal structure The reason for a higher kinetic constant for the
sample annealed at 600 degC was probably the presence of the rutile phase The best
photocatalytic activity shows sample annealed at 650 degC due to the optimum ratio of
anataserutile phase The worst photocatalytic performance was exhibited by the sample
annealed at 700 degC and this can be explained by the collapse of the nanotubular morphology
and porosity loss combined with the disappearance of the anatase phase (Fig 2) The
advantages of the mixed anatase-rutile phase could be due to the efficient trapping and
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
48
separation of photogenerated charges at the phase junction or the separation of the charges
across different crystallite phases [30]
Fig 7 Effect of sintered TiO2 nanotubes on the photocatalytic MO degradation (a) and
photocatalytic kinetic behavior of the degradation of MO by sintered TiO2 nanotubes (b)
4 Conclusions
In this study a highly ordered TiO2 nanotube array on a Ti substrate was successfully
fabricated using electrochemical anodization It was observed that the morphologies and
crystallinity of the TiO2 nanotube array were greatly influenced by the sintering temperature
It was shown the sample annealed at 450 degC consisted mostly of the anatase phase while 994
of rutile was formed at 700 degC At the temperatures of 600 degC and 650 degC a mixture of
anatase and rutile was observed Different amounts of the polymorph phase strongly
influenced the photodegradation of the MO dye It was established that the TiO2 nanotube
array sintered at 650 degC showed the best photocatalytic activity due to the optimal anatase-to-
rutile ratio With a further increase in temperature up to 700 degC the photocatalytic activity
drastically decreased due to the collapse of the nanotubular structure and the excessive rutile
content As a result of the presented investigation an appropriate tailoring of the ratio of
polymorph phases in TiO2 nanotubes could lead to a more suitable photocatalyst
Acknowledgements
This research was supported by the project OI 172057 and project III 45019 of the
Ministry of Education Science and Technological Development of the Republic of Serbia
and by NSF CREST (HRD-0833184) NASA (NNX09AV07A) and NSF-PREM1523617
awards The work in Lausanne was supported by grants from Switzerland through the Swiss
Contribution (SH7220) E H wants to thank the AIT grant the Zeno-Karl Schindler
foundation and MBR Global Water Initiatives for their support
5 References
1 X Chen Z Wu D Liu and Z Gao Nanoscale Res Lett 12 1 (2017) 143
2 E Bailoacuten-Garciacutea A Elmouwahidi F Carrasco-Mariacuten A F Peacuterez-Cadenas and F J
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
49
Maldonado-Hoacutedar Appl Catal B Environ 217 (2017) 540-550
3 H Zhang X Chen Z Li J Kou T Yu and Z Zou J Phys D Appl Phys 40 21
(2007) 6846-6849
4 M Sabarinathan S Harish J Archana M Navaneethan H Ikeda and Y
Hayakawa RSC Adv 7 40 (2017) 24754-24763
5 M R Hoffmann S T Martin W Choi and D W Bahnemann Chem Rev 95 1
(1995) 69-96
6 K Nakata and A Fujishima J Photochem Photobiol C Photochem Rev 13 3
(2012) 169-189
7 D Fang Z Luo K Huang and D C Lagoudas Appl Surf Sci 257 15 (2011)
6451-6461
8 J M Macak M Zlamal J Krysa and P Schmuki Small 3 2 (2007) 300-304
9 Y Lai L Sun Y Chen H Zhuang C Lin and J W Chin J Electrochem Soc
153 7 (2006) D123
10 Y Sun K Yan G Wang W Guo and T Ma J Phys Chem C 115 26 (2011)
12844-12849
11 H J Oh J H Lee Y J Kim S J Suh J H Lee and C S Chi Appl Catal B
Environ 84 1ndash2 (2008) 142-147
12 N Masahashi Y Mizukoshi S Semboshi and N Ohtsu Appl Catal B Environ
901ndash2 (2009) 255-261
13 J Zhang Q Xu Z Feng M Li and C Li Angew Chemie Int Ed 47 9 (2008)
1766-1769
14 J Yu and B Wang Appl Catal B Environ 94 3ndash4 (2010) 295-302
15 O Carp C L Huisman and A Reller Prog Solid State Chem 32 1ndash2 (2004) 33-
177
16 B D Cullity Elements of x-ray diffraction Reading MA Addison-Wesley
Publishing Company Inc 1978
17 A G Kontos et al Chem Phys Lett 490 1ndash3 (2010) 58-62
18 Z Su and W Zhou J Mater Chem 21 25 (2011) 8955
19 G K Mor O K Varghese M Paulose K Shankar and C a Grimes Sol Energy
Mater Sol Cells 90 14 (2006) 2011-2075
20 Y Li et al Appl Surf Sci 297 (2014) 103-108
21 T Ohsaka F Izumi and Y Fujiki J Raman Spectrosc 7 6 (1978) 321-324
22 W F Zhang Y L He M S Zhang Z Yin and Q Chen J Phys D Appl Phys
33 8 (2000) 912-916
23 H C Choi Y M Jung and S Bin Kim Vib Spectrosc 37 1 (2005) 33-38
24 Y Hara and M Nicol Phys Status Solidi 94 1 (1979) 317-322
25 B Santara P K Giri K Imakita and M Fujii J Phys D Appl Phys47 21 (2014)
215302
26 Z Lou Y Li H Song Z Ye and L Zhu RSC Adv 6 51 (2016) 45343-45348
27 X Zhu J Chen X Yu X Zhu X Gao and K Cen RSC Adv 5 39 (2015) 30416-
30424
28 Y Fu H Du S Zhang and W Huang Mater Sci Eng A 403 1ndash2 (2005) 25-31
29 Z Fan H Guo K Fang and Y Sun RSC Adv 5 31 (2015) 24795-24802
30 Y K Kho A Iwase W Y Teoh L Madler A Kudo and R Amal J Phys Chem
C 114 6 (2010) 2821-2829
Садржај Једнодимензионе наноцеви TiO2 усправно орјентисане на супстрат добијене
су електрохемијском анодизацијом титанијумске фолије у киселом електролиту У
циљу промене кристалне структуре и морфологије филма анодизовани аморфни
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
50
филмови TiO2 синтеровани су на високој температури Морфолошка промена
посматрана је скенирајућом електронском микроскопијом (СЕМ) док је кристална
структура испитивана рендгенском анализом (ХРД) и Раманском спектроскопијом
Хемијски састав је урађен помоћу спектроскопске фотоемисије X-зрака (ХПС) У овом
раду је испитиван утицај кристалне структуре и морфологије нанотубуларног филма
TiO2 на фотокаталитичку деградацију воденог раствора метил оранжа (МО) под
дејством ултраљубичастог зрачења Наноцеви TiO2 синтероване на 650 degC 30 мин
показују најбољу кристалоичност и фотокаталитичку активност у поређењу са
осталим филмовима TiO2
Кључне речи Титанијум диоксид анодизација синтеровање кристална фаза
фотокатализа
copy 2016 Authors Published by the International Institute for the Science of Sintering This
article is an open access article distributed under the terms and conditions of the Creative
Commons mdash Attribution 40 International license
(httpscreativecommonsorglicensesby40)
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
41
The morphology evolution was studied using scanning electron microscopy (FEI
NanoSEM 630 15keV)
Raman spectra were obtained in the range from 100 to 1100 cm-1 with a Horiba Jobin
Yvon Aramis RamanPL System using a He-Ne laser operating at 6328 nm with the power
of 1 mW on the sample surface All measurements were performed using a grating with 1800
linesmm a 100times microscope objective and the acquisition of 10s5 cycles
The X-ray Diffraction (XRD) patterns were obtained on a Philips PW-1050
diffractometer operated at 40 kV and 30 mA using Ni-filtered Cu K radiation (15419 Aring)
BraggndashBrentano focusing geometry was used with a fixed 1deg divergence and 01deg receiving
slits The patterns were taken in the 20ndash80deg 2 range with the step of 005deg and collection
time of 1 s per step The crystalline sizes were estimated using Scherrerʼs equation [16] D = k
(βcosθ) where D was crystalline size k the Sherrerʼs constant λ the wavelength of X-ray
radiation β the full-width at half-maximum (FWHM) and θ was the diffraction angle
The XPS measurements were conducted on a Kratos Axis Ultra XPS system with
Monochromated Aluminum K-Alpha X-Rays (h = 14866 eV) During the measurement
chamber vacuum was at 25 times 10-8 torrs The X-Ray gun was operated at 15 kW and 10 mA
A charge neutralizer was used to reduce the charging effects from non-conducting surfaces
All survey scans were collected with a Pass Energy of 160 eV and one sweep (or averaging)
All Region scans were made with a Pass Energy of 20 eV and the number of sweeps
(averages) performed was dependent on the measured region All data was calibrated to the
C-C portion of the C1s peak at 2845 eV
The photocatalytic activity of TiO2 nanotube films on titanium foil was investigated
by immersing the samples into 3 ml of aqueous MO solution (concentration of 5 mgL) In
order to the achieve adsorptiondesorption equilibrium the samples were left in solution for 1
h in the dark prior to the photocatalytic test reaction The sample was illuminated by a spot
light source (Hamamatsu LC5) from a distance of 1 cm (light intensity 52 mWcm2) The
decomposition rate of MO as a function of irradiation time was measured by a Varian Cary 50
Scan UV-Vis spectrophotometer In order to determine the intrinsic photolysis of MO (ie the
UV light-induced self-decomposition) the aqueous solution of MO without photocatalysts
was irradiated
3 Results and Discussion
The anodization of Ti foil is a promising approach to fabricating vertically oriented
TiO2 nanotube arrays directly grown on the Ti substrate without a template The sintering
temperature is an important parameter that affects the morphology and crystallinity of
nanotubes Fig 1 (a-j) shows the evolution of the nanotube morphology as a consequence of
sintering temperature change Tab I shows the influence of the annealing temperature on the
average inner diameter (Di) the wall thickness (W) and the tube length (L) obtained using the
image analysis software The porosity was calculated according to the equation [17]
223
21
WDi
WDiWP
Fig 1a and b show well-defined TiO2 nanotubes formed in an aqueous solution of HF
at a potential of 15 V It is evident that the highly ordered nanotube array consists of very
regular tubes with an average inner diameter of 90 nm and a wall thickness of 10 nm The
length of the tubes is 315 nm with rough walls typical of nanotubes grown in an electrolyte
with water [18] After annealing at 450 degC nanotubular arrays retained their structural
integrity with a slight change in the diameters wall thickness and length as it is shown in
Tab I At 600 degC a compact layer appeared at the interface between the TiO2 nanotubes and
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
42
the titanium foil and due to that the length of nanotubes decrease on L = 220 nm With further
increase in temperature the diameters slightly decreased while the length shortened
drastically This can be presumably ascribed to the sintering process that occurs during
crystallization At 700degC nanotubes no longer had a regular shape with recognizable
particles grown from the nanotubes With sintering the porosity lowered (Tab I) due to the
shrinking of the tubes which merged together reducing the spacing between the walls
Tab I Average morphological parameters for as-anodized and sintered TiO2 nanotubes
Samples Di (nm) W (nm) L (nm) P
As-anodized 90 10 314 070
450 oC 75 13 315 060
600 oC 84 13 222 062
650 oC 72 16 152 053
700 oC 105
Fig 1 SEM micrographs of the top and side views of TiO2 nanotubes sintered at different
temperatures (a and b) as-anodized (c and d) 450 degC (e and f) 600 degC (g and h) 650 degC (i
and j) 700 degC
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
43
In order to determine the phase composition and crystallinity of TiO2 nanotube arrays
at different sintering temperatures the XRD diffractograms and Raman spectra were studied
Fig 2 shows the diffractograms of TiO2 nanotube arrays annealed at a different temperature
The as-anodized TiO2 nanotubes are amorphous due to which only the peaks of the titanium
substrate are present in the diffractogram With annealing TiO2 nanotubes crystallized in two
polymorphous forms anatase and rutile At 450 degC anatase was observed as the main crystal
phase due to the presence of two main anatase peaks at 253deg and 48deg corresponding to the
(101) and (200) planes respectively Also a small amount of the rutile phase appeared at
273deg (110) All other peaks came from the substrate which dominated due to the low
thickness of the film Mor at al [19] reported that in nanotubes on a titanium substrate rutile
appeared at 430 degC while in nanotubes on conductive glass annealed at 500 degC rutile did not
appear This happened due to the growth of rutile crystallites at the interface between the
nanotube bottom and the thermally oxidized Ti substrate [7] With temperature rise to 600 degC
new peaks appeared at 361deg (101) 414deg (111) 44deg (210) 543deg (211) 567deg (220) and 689deg
(301) which corresponded to the rutile phase With further temperature increase up to 650
and 700 degC the intensity of the rutile peaks gradually strengthened while the intensity of
peaks from anatase decreased proving that almost all anatase transformed into rutile A
decrease of the diffraction intensity of the titanium foil was also observed revealing the
crystallization of the support [20] The phase composition and the crystallite size estimated
using Scherrerʼs formula are shown in Tab II The crystal size of anatase and rutile was
growing until the temperature reached 650 degC when it started to drop probably due to the
collapse of the nanotube structure
Fig 2 XRD patterns of the as-anodized and sintered TiO2 nanotubes (A-anatase R-rutile Ti-
titanium)
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
44
Tab II Phase composition and average crystallite size of annealed TiO2 nanotubes
Temperature
of annealing oC
Amount of
anatase phase
Amount of
rutile phase
Crystallite size
for anatase
(101)
Crystallite size
for rutile
(110)
450 997 03 231 54
600 203 797 289 257
650 25 975 262 346
700 06 994 242 273
The temperature-induced anatase and rutile crystal modifications of TiO2 were
tracked using spectroscopy methods The Raman spectrum of the sample annealed at 450 degC
(Fig 3) showed only the Raman peaks characteristic for the crystal modification of anatase at
145 cm-1 (Eg(1) mode) 198 cm-1 (Eg(2) mode) and 395 cm-1 (B1g(1) mode) as well as the
peak at 515 cm-1 that corresponds to the superposition of the A1g and B1g(2) modes and the
peak at 635 cm-1 which comes from the Eg(3) mode [21-23] With an increase in temperature
new peaks started to appear in the Raman spectra along with anatase peaks At 600 degC the
rutile Eg mode at 425 cm-1 occurred besides the anatase modes Further temperature increase
up to 650 degC resulted in more intensive rutile peaks while the intensity of all the major
anatase modes decreased and only the main anatase mode at 145 cm-1 remained clearly
visible
Fig 3 Raman spectra of annealed TiO2 nanotubes (A-anatase R-rutile)
The rutile phase was observed as the dominant one identified by the Eg mode at 446 cm-
1and A1g mode at 609 cm-1 as well as by the broad peak at 242 cm-1 which originated from
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
45
the second-order vibrational mode Eg (SO) and disorder effects [24 25] At 700 degC the main
anatase mode was replaced with the rutile B1g mode at 142 cm-1 indicating that anatase
phase completely disappeared The whole spectrum at this temperature was assigned to the
rutile phase where the four Raman modes were prominent enough (B1g Eg A1g and Eg (SO))
while the mode expected at 826-827 cm-1 was too weak to be observed
An XPS study was further employed in order to investigate how different annealing
temperatures influenced the chemical composition of anodized titanium foil The results are
presented in Fig 4 In pristine TiO2 titanium (Ti 2p) oxygen (O1s) carbon (C1s) nitrogen
(N1s) fluoride (F1s) and lead (4f) XPS peaks were noticed After a heat treatment peaks of
lead fluoride and nitrogen disappeared proving that they were caused by surface
contamination No significant changes were noticed for the samples annealed at 450 and 600
degC relative to pristine samples Since the positions of Ti 2p32 and Ti 2p12 peaks (Fig 5) in
these samples ranged from 45816 to 45837 eV and from 46385 to 46410 eV respectively
it clearly indicated the existence of a Ti4+ state [26 27] Moreover the difference in the
binding energy of Ti 2p32 and Ti 2p12 peaks in all of the annealed samples was in accordance
with the literature data for the mentioned state of titanium Although at higher annealing
temperatures both peaks shifted slightly towards lower binding energies their positions still
remained well above the binding energy of the Ti3+ state [27 28] In the O1s regions of
binding energy the peak at 5296-5297 eV proved O-Ti4+ bonding (Fig 6) [29] It was
possible to assign it to the lattice oxygen in TiO2 On the other hand the shoulder effect that
could be fitted with the peak at 5310 plusmn 02 eV probably originated from surface-adsorbed
oxygen (within the hydroxyl groups at the outermost surface as well as within the adsorbed
water resulting from moisture adsorption in air) [29] The increase in annealing temperature
up to 650 degC caused the reduction of the surface-adsorbed oxygen content The atomic ratio
OlattTi2p provides an insight into the stoichiometry of the structure
Fig 4 XPS survey spectrum for as-anodized TiO2 and sintered TiO2
The results show the substoichiometric structure for the amorphous (as-anodized) sample
(Tab III) which probably indicates the presence of oxygen vacancies in it It can be assumed
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
46
that after annealing the filling of oxygen defects proceeded which was assisted by the
crystallization process since annealing was taking place in air
Fig 5 XPS spectrum for Ti 2p peak for as-anodized and sintered TiO2
Tab III XPS results of as-anodized and sintered TiO2
Samples OlattOtot
(area )
OadsOtot
(area )
OlattTi2p
(atomic ratio)
BE(Ti2p12)-BE(Ti2p32)
(eV)
As-
anodized
587 413 16 577
450 oC 799 201 21 573
600 oC 820 180 21 572
650 oC 843 157 21 569
700 oC 815 185 21 572
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
47
Fig 6 XPS spectrum for O 1s peak for as-anodized and sintered TiO2
Tab IV Influence of sintering temperature on photocatalytic degradation ndash first-order rate
constant and correlation coefficient
Temperature of
annealing oC
|k| x 10-2
min-1
R2
450 109 096
600 111 098
650 124 094
700 062 090
The influence of the sintering temperature of TiO2 nanotubes on the degradation of the MO
textile dye is shown on Fig 7a A further analysis indicated that the reaction could be
presented as ln(CCo) = ln(AAo) = kt where Co was the initial dye concentration C was the
concentration after irradiation for time t Ao and A were the corresponding absorbance while k
was a rate constant Fig 7b shows the linear curves proving that the degradation of MB by
sintered TiO2 nanotubes follows the pseudo-first order kinetic The first-order constant k and
the correlation coefficient R2 are shown in Tab IV It is evident that an increased annealing
temperature was accompanied by the increase of k up to 700 degC when it began to decrease
gradually The samples sintered at 450 degC and 600 degC had similar morphology parameters but
there was a difference in the crystal structure The reason for a higher kinetic constant for the
sample annealed at 600 degC was probably the presence of the rutile phase The best
photocatalytic activity shows sample annealed at 650 degC due to the optimum ratio of
anataserutile phase The worst photocatalytic performance was exhibited by the sample
annealed at 700 degC and this can be explained by the collapse of the nanotubular morphology
and porosity loss combined with the disappearance of the anatase phase (Fig 2) The
advantages of the mixed anatase-rutile phase could be due to the efficient trapping and
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
48
separation of photogenerated charges at the phase junction or the separation of the charges
across different crystallite phases [30]
Fig 7 Effect of sintered TiO2 nanotubes on the photocatalytic MO degradation (a) and
photocatalytic kinetic behavior of the degradation of MO by sintered TiO2 nanotubes (b)
4 Conclusions
In this study a highly ordered TiO2 nanotube array on a Ti substrate was successfully
fabricated using electrochemical anodization It was observed that the morphologies and
crystallinity of the TiO2 nanotube array were greatly influenced by the sintering temperature
It was shown the sample annealed at 450 degC consisted mostly of the anatase phase while 994
of rutile was formed at 700 degC At the temperatures of 600 degC and 650 degC a mixture of
anatase and rutile was observed Different amounts of the polymorph phase strongly
influenced the photodegradation of the MO dye It was established that the TiO2 nanotube
array sintered at 650 degC showed the best photocatalytic activity due to the optimal anatase-to-
rutile ratio With a further increase in temperature up to 700 degC the photocatalytic activity
drastically decreased due to the collapse of the nanotubular structure and the excessive rutile
content As a result of the presented investigation an appropriate tailoring of the ratio of
polymorph phases in TiO2 nanotubes could lead to a more suitable photocatalyst
Acknowledgements
This research was supported by the project OI 172057 and project III 45019 of the
Ministry of Education Science and Technological Development of the Republic of Serbia
and by NSF CREST (HRD-0833184) NASA (NNX09AV07A) and NSF-PREM1523617
awards The work in Lausanne was supported by grants from Switzerland through the Swiss
Contribution (SH7220) E H wants to thank the AIT grant the Zeno-Karl Schindler
foundation and MBR Global Water Initiatives for their support
5 References
1 X Chen Z Wu D Liu and Z Gao Nanoscale Res Lett 12 1 (2017) 143
2 E Bailoacuten-Garciacutea A Elmouwahidi F Carrasco-Mariacuten A F Peacuterez-Cadenas and F J
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
49
Maldonado-Hoacutedar Appl Catal B Environ 217 (2017) 540-550
3 H Zhang X Chen Z Li J Kou T Yu and Z Zou J Phys D Appl Phys 40 21
(2007) 6846-6849
4 M Sabarinathan S Harish J Archana M Navaneethan H Ikeda and Y
Hayakawa RSC Adv 7 40 (2017) 24754-24763
5 M R Hoffmann S T Martin W Choi and D W Bahnemann Chem Rev 95 1
(1995) 69-96
6 K Nakata and A Fujishima J Photochem Photobiol C Photochem Rev 13 3
(2012) 169-189
7 D Fang Z Luo K Huang and D C Lagoudas Appl Surf Sci 257 15 (2011)
6451-6461
8 J M Macak M Zlamal J Krysa and P Schmuki Small 3 2 (2007) 300-304
9 Y Lai L Sun Y Chen H Zhuang C Lin and J W Chin J Electrochem Soc
153 7 (2006) D123
10 Y Sun K Yan G Wang W Guo and T Ma J Phys Chem C 115 26 (2011)
12844-12849
11 H J Oh J H Lee Y J Kim S J Suh J H Lee and C S Chi Appl Catal B
Environ 84 1ndash2 (2008) 142-147
12 N Masahashi Y Mizukoshi S Semboshi and N Ohtsu Appl Catal B Environ
901ndash2 (2009) 255-261
13 J Zhang Q Xu Z Feng M Li and C Li Angew Chemie Int Ed 47 9 (2008)
1766-1769
14 J Yu and B Wang Appl Catal B Environ 94 3ndash4 (2010) 295-302
15 O Carp C L Huisman and A Reller Prog Solid State Chem 32 1ndash2 (2004) 33-
177
16 B D Cullity Elements of x-ray diffraction Reading MA Addison-Wesley
Publishing Company Inc 1978
17 A G Kontos et al Chem Phys Lett 490 1ndash3 (2010) 58-62
18 Z Su and W Zhou J Mater Chem 21 25 (2011) 8955
19 G K Mor O K Varghese M Paulose K Shankar and C a Grimes Sol Energy
Mater Sol Cells 90 14 (2006) 2011-2075
20 Y Li et al Appl Surf Sci 297 (2014) 103-108
21 T Ohsaka F Izumi and Y Fujiki J Raman Spectrosc 7 6 (1978) 321-324
22 W F Zhang Y L He M S Zhang Z Yin and Q Chen J Phys D Appl Phys
33 8 (2000) 912-916
23 H C Choi Y M Jung and S Bin Kim Vib Spectrosc 37 1 (2005) 33-38
24 Y Hara and M Nicol Phys Status Solidi 94 1 (1979) 317-322
25 B Santara P K Giri K Imakita and M Fujii J Phys D Appl Phys47 21 (2014)
215302
26 Z Lou Y Li H Song Z Ye and L Zhu RSC Adv 6 51 (2016) 45343-45348
27 X Zhu J Chen X Yu X Zhu X Gao and K Cen RSC Adv 5 39 (2015) 30416-
30424
28 Y Fu H Du S Zhang and W Huang Mater Sci Eng A 403 1ndash2 (2005) 25-31
29 Z Fan H Guo K Fang and Y Sun RSC Adv 5 31 (2015) 24795-24802
30 Y K Kho A Iwase W Y Teoh L Madler A Kudo and R Amal J Phys Chem
C 114 6 (2010) 2821-2829
Садржај Једнодимензионе наноцеви TiO2 усправно орјентисане на супстрат добијене
су електрохемијском анодизацијом титанијумске фолије у киселом електролиту У
циљу промене кристалне структуре и морфологије филма анодизовани аморфни
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
50
филмови TiO2 синтеровани су на високој температури Морфолошка промена
посматрана је скенирајућом електронском микроскопијом (СЕМ) док је кристална
структура испитивана рендгенском анализом (ХРД) и Раманском спектроскопијом
Хемијски састав је урађен помоћу спектроскопске фотоемисије X-зрака (ХПС) У овом
раду је испитиван утицај кристалне структуре и морфологије нанотубуларног филма
TiO2 на фотокаталитичку деградацију воденог раствора метил оранжа (МО) под
дејством ултраљубичастог зрачења Наноцеви TiO2 синтероване на 650 degC 30 мин
показују најбољу кристалоичност и фотокаталитичку активност у поређењу са
осталим филмовима TiO2
Кључне речи Титанијум диоксид анодизација синтеровање кристална фаза
фотокатализа
copy 2016 Authors Published by the International Institute for the Science of Sintering This
article is an open access article distributed under the terms and conditions of the Creative
Commons mdash Attribution 40 International license
(httpscreativecommonsorglicensesby40)
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
42
the titanium foil and due to that the length of nanotubes decrease on L = 220 nm With further
increase in temperature the diameters slightly decreased while the length shortened
drastically This can be presumably ascribed to the sintering process that occurs during
crystallization At 700degC nanotubes no longer had a regular shape with recognizable
particles grown from the nanotubes With sintering the porosity lowered (Tab I) due to the
shrinking of the tubes which merged together reducing the spacing between the walls
Tab I Average morphological parameters for as-anodized and sintered TiO2 nanotubes
Samples Di (nm) W (nm) L (nm) P
As-anodized 90 10 314 070
450 oC 75 13 315 060
600 oC 84 13 222 062
650 oC 72 16 152 053
700 oC 105
Fig 1 SEM micrographs of the top and side views of TiO2 nanotubes sintered at different
temperatures (a and b) as-anodized (c and d) 450 degC (e and f) 600 degC (g and h) 650 degC (i
and j) 700 degC
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
43
In order to determine the phase composition and crystallinity of TiO2 nanotube arrays
at different sintering temperatures the XRD diffractograms and Raman spectra were studied
Fig 2 shows the diffractograms of TiO2 nanotube arrays annealed at a different temperature
The as-anodized TiO2 nanotubes are amorphous due to which only the peaks of the titanium
substrate are present in the diffractogram With annealing TiO2 nanotubes crystallized in two
polymorphous forms anatase and rutile At 450 degC anatase was observed as the main crystal
phase due to the presence of two main anatase peaks at 253deg and 48deg corresponding to the
(101) and (200) planes respectively Also a small amount of the rutile phase appeared at
273deg (110) All other peaks came from the substrate which dominated due to the low
thickness of the film Mor at al [19] reported that in nanotubes on a titanium substrate rutile
appeared at 430 degC while in nanotubes on conductive glass annealed at 500 degC rutile did not
appear This happened due to the growth of rutile crystallites at the interface between the
nanotube bottom and the thermally oxidized Ti substrate [7] With temperature rise to 600 degC
new peaks appeared at 361deg (101) 414deg (111) 44deg (210) 543deg (211) 567deg (220) and 689deg
(301) which corresponded to the rutile phase With further temperature increase up to 650
and 700 degC the intensity of the rutile peaks gradually strengthened while the intensity of
peaks from anatase decreased proving that almost all anatase transformed into rutile A
decrease of the diffraction intensity of the titanium foil was also observed revealing the
crystallization of the support [20] The phase composition and the crystallite size estimated
using Scherrerʼs formula are shown in Tab II The crystal size of anatase and rutile was
growing until the temperature reached 650 degC when it started to drop probably due to the
collapse of the nanotube structure
Fig 2 XRD patterns of the as-anodized and sintered TiO2 nanotubes (A-anatase R-rutile Ti-
titanium)
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
44
Tab II Phase composition and average crystallite size of annealed TiO2 nanotubes
Temperature
of annealing oC
Amount of
anatase phase
Amount of
rutile phase
Crystallite size
for anatase
(101)
Crystallite size
for rutile
(110)
450 997 03 231 54
600 203 797 289 257
650 25 975 262 346
700 06 994 242 273
The temperature-induced anatase and rutile crystal modifications of TiO2 were
tracked using spectroscopy methods The Raman spectrum of the sample annealed at 450 degC
(Fig 3) showed only the Raman peaks characteristic for the crystal modification of anatase at
145 cm-1 (Eg(1) mode) 198 cm-1 (Eg(2) mode) and 395 cm-1 (B1g(1) mode) as well as the
peak at 515 cm-1 that corresponds to the superposition of the A1g and B1g(2) modes and the
peak at 635 cm-1 which comes from the Eg(3) mode [21-23] With an increase in temperature
new peaks started to appear in the Raman spectra along with anatase peaks At 600 degC the
rutile Eg mode at 425 cm-1 occurred besides the anatase modes Further temperature increase
up to 650 degC resulted in more intensive rutile peaks while the intensity of all the major
anatase modes decreased and only the main anatase mode at 145 cm-1 remained clearly
visible
Fig 3 Raman spectra of annealed TiO2 nanotubes (A-anatase R-rutile)
The rutile phase was observed as the dominant one identified by the Eg mode at 446 cm-
1and A1g mode at 609 cm-1 as well as by the broad peak at 242 cm-1 which originated from
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
45
the second-order vibrational mode Eg (SO) and disorder effects [24 25] At 700 degC the main
anatase mode was replaced with the rutile B1g mode at 142 cm-1 indicating that anatase
phase completely disappeared The whole spectrum at this temperature was assigned to the
rutile phase where the four Raman modes were prominent enough (B1g Eg A1g and Eg (SO))
while the mode expected at 826-827 cm-1 was too weak to be observed
An XPS study was further employed in order to investigate how different annealing
temperatures influenced the chemical composition of anodized titanium foil The results are
presented in Fig 4 In pristine TiO2 titanium (Ti 2p) oxygen (O1s) carbon (C1s) nitrogen
(N1s) fluoride (F1s) and lead (4f) XPS peaks were noticed After a heat treatment peaks of
lead fluoride and nitrogen disappeared proving that they were caused by surface
contamination No significant changes were noticed for the samples annealed at 450 and 600
degC relative to pristine samples Since the positions of Ti 2p32 and Ti 2p12 peaks (Fig 5) in
these samples ranged from 45816 to 45837 eV and from 46385 to 46410 eV respectively
it clearly indicated the existence of a Ti4+ state [26 27] Moreover the difference in the
binding energy of Ti 2p32 and Ti 2p12 peaks in all of the annealed samples was in accordance
with the literature data for the mentioned state of titanium Although at higher annealing
temperatures both peaks shifted slightly towards lower binding energies their positions still
remained well above the binding energy of the Ti3+ state [27 28] In the O1s regions of
binding energy the peak at 5296-5297 eV proved O-Ti4+ bonding (Fig 6) [29] It was
possible to assign it to the lattice oxygen in TiO2 On the other hand the shoulder effect that
could be fitted with the peak at 5310 plusmn 02 eV probably originated from surface-adsorbed
oxygen (within the hydroxyl groups at the outermost surface as well as within the adsorbed
water resulting from moisture adsorption in air) [29] The increase in annealing temperature
up to 650 degC caused the reduction of the surface-adsorbed oxygen content The atomic ratio
OlattTi2p provides an insight into the stoichiometry of the structure
Fig 4 XPS survey spectrum for as-anodized TiO2 and sintered TiO2
The results show the substoichiometric structure for the amorphous (as-anodized) sample
(Tab III) which probably indicates the presence of oxygen vacancies in it It can be assumed
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
46
that after annealing the filling of oxygen defects proceeded which was assisted by the
crystallization process since annealing was taking place in air
Fig 5 XPS spectrum for Ti 2p peak for as-anodized and sintered TiO2
Tab III XPS results of as-anodized and sintered TiO2
Samples OlattOtot
(area )
OadsOtot
(area )
OlattTi2p
(atomic ratio)
BE(Ti2p12)-BE(Ti2p32)
(eV)
As-
anodized
587 413 16 577
450 oC 799 201 21 573
600 oC 820 180 21 572
650 oC 843 157 21 569
700 oC 815 185 21 572
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
47
Fig 6 XPS spectrum for O 1s peak for as-anodized and sintered TiO2
Tab IV Influence of sintering temperature on photocatalytic degradation ndash first-order rate
constant and correlation coefficient
Temperature of
annealing oC
|k| x 10-2
min-1
R2
450 109 096
600 111 098
650 124 094
700 062 090
The influence of the sintering temperature of TiO2 nanotubes on the degradation of the MO
textile dye is shown on Fig 7a A further analysis indicated that the reaction could be
presented as ln(CCo) = ln(AAo) = kt where Co was the initial dye concentration C was the
concentration after irradiation for time t Ao and A were the corresponding absorbance while k
was a rate constant Fig 7b shows the linear curves proving that the degradation of MB by
sintered TiO2 nanotubes follows the pseudo-first order kinetic The first-order constant k and
the correlation coefficient R2 are shown in Tab IV It is evident that an increased annealing
temperature was accompanied by the increase of k up to 700 degC when it began to decrease
gradually The samples sintered at 450 degC and 600 degC had similar morphology parameters but
there was a difference in the crystal structure The reason for a higher kinetic constant for the
sample annealed at 600 degC was probably the presence of the rutile phase The best
photocatalytic activity shows sample annealed at 650 degC due to the optimum ratio of
anataserutile phase The worst photocatalytic performance was exhibited by the sample
annealed at 700 degC and this can be explained by the collapse of the nanotubular morphology
and porosity loss combined with the disappearance of the anatase phase (Fig 2) The
advantages of the mixed anatase-rutile phase could be due to the efficient trapping and
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
48
separation of photogenerated charges at the phase junction or the separation of the charges
across different crystallite phases [30]
Fig 7 Effect of sintered TiO2 nanotubes on the photocatalytic MO degradation (a) and
photocatalytic kinetic behavior of the degradation of MO by sintered TiO2 nanotubes (b)
4 Conclusions
In this study a highly ordered TiO2 nanotube array on a Ti substrate was successfully
fabricated using electrochemical anodization It was observed that the morphologies and
crystallinity of the TiO2 nanotube array were greatly influenced by the sintering temperature
It was shown the sample annealed at 450 degC consisted mostly of the anatase phase while 994
of rutile was formed at 700 degC At the temperatures of 600 degC and 650 degC a mixture of
anatase and rutile was observed Different amounts of the polymorph phase strongly
influenced the photodegradation of the MO dye It was established that the TiO2 nanotube
array sintered at 650 degC showed the best photocatalytic activity due to the optimal anatase-to-
rutile ratio With a further increase in temperature up to 700 degC the photocatalytic activity
drastically decreased due to the collapse of the nanotubular structure and the excessive rutile
content As a result of the presented investigation an appropriate tailoring of the ratio of
polymorph phases in TiO2 nanotubes could lead to a more suitable photocatalyst
Acknowledgements
This research was supported by the project OI 172057 and project III 45019 of the
Ministry of Education Science and Technological Development of the Republic of Serbia
and by NSF CREST (HRD-0833184) NASA (NNX09AV07A) and NSF-PREM1523617
awards The work in Lausanne was supported by grants from Switzerland through the Swiss
Contribution (SH7220) E H wants to thank the AIT grant the Zeno-Karl Schindler
foundation and MBR Global Water Initiatives for their support
5 References
1 X Chen Z Wu D Liu and Z Gao Nanoscale Res Lett 12 1 (2017) 143
2 E Bailoacuten-Garciacutea A Elmouwahidi F Carrasco-Mariacuten A F Peacuterez-Cadenas and F J
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
49
Maldonado-Hoacutedar Appl Catal B Environ 217 (2017) 540-550
3 H Zhang X Chen Z Li J Kou T Yu and Z Zou J Phys D Appl Phys 40 21
(2007) 6846-6849
4 M Sabarinathan S Harish J Archana M Navaneethan H Ikeda and Y
Hayakawa RSC Adv 7 40 (2017) 24754-24763
5 M R Hoffmann S T Martin W Choi and D W Bahnemann Chem Rev 95 1
(1995) 69-96
6 K Nakata and A Fujishima J Photochem Photobiol C Photochem Rev 13 3
(2012) 169-189
7 D Fang Z Luo K Huang and D C Lagoudas Appl Surf Sci 257 15 (2011)
6451-6461
8 J M Macak M Zlamal J Krysa and P Schmuki Small 3 2 (2007) 300-304
9 Y Lai L Sun Y Chen H Zhuang C Lin and J W Chin J Electrochem Soc
153 7 (2006) D123
10 Y Sun K Yan G Wang W Guo and T Ma J Phys Chem C 115 26 (2011)
12844-12849
11 H J Oh J H Lee Y J Kim S J Suh J H Lee and C S Chi Appl Catal B
Environ 84 1ndash2 (2008) 142-147
12 N Masahashi Y Mizukoshi S Semboshi and N Ohtsu Appl Catal B Environ
901ndash2 (2009) 255-261
13 J Zhang Q Xu Z Feng M Li and C Li Angew Chemie Int Ed 47 9 (2008)
1766-1769
14 J Yu and B Wang Appl Catal B Environ 94 3ndash4 (2010) 295-302
15 O Carp C L Huisman and A Reller Prog Solid State Chem 32 1ndash2 (2004) 33-
177
16 B D Cullity Elements of x-ray diffraction Reading MA Addison-Wesley
Publishing Company Inc 1978
17 A G Kontos et al Chem Phys Lett 490 1ndash3 (2010) 58-62
18 Z Su and W Zhou J Mater Chem 21 25 (2011) 8955
19 G K Mor O K Varghese M Paulose K Shankar and C a Grimes Sol Energy
Mater Sol Cells 90 14 (2006) 2011-2075
20 Y Li et al Appl Surf Sci 297 (2014) 103-108
21 T Ohsaka F Izumi and Y Fujiki J Raman Spectrosc 7 6 (1978) 321-324
22 W F Zhang Y L He M S Zhang Z Yin and Q Chen J Phys D Appl Phys
33 8 (2000) 912-916
23 H C Choi Y M Jung and S Bin Kim Vib Spectrosc 37 1 (2005) 33-38
24 Y Hara and M Nicol Phys Status Solidi 94 1 (1979) 317-322
25 B Santara P K Giri K Imakita and M Fujii J Phys D Appl Phys47 21 (2014)
215302
26 Z Lou Y Li H Song Z Ye and L Zhu RSC Adv 6 51 (2016) 45343-45348
27 X Zhu J Chen X Yu X Zhu X Gao and K Cen RSC Adv 5 39 (2015) 30416-
30424
28 Y Fu H Du S Zhang and W Huang Mater Sci Eng A 403 1ndash2 (2005) 25-31
29 Z Fan H Guo K Fang and Y Sun RSC Adv 5 31 (2015) 24795-24802
30 Y K Kho A Iwase W Y Teoh L Madler A Kudo and R Amal J Phys Chem
C 114 6 (2010) 2821-2829
Садржај Једнодимензионе наноцеви TiO2 усправно орјентисане на супстрат добијене
су електрохемијском анодизацијом титанијумске фолије у киселом електролиту У
циљу промене кристалне структуре и морфологије филма анодизовани аморфни
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
50
филмови TiO2 синтеровани су на високој температури Морфолошка промена
посматрана је скенирајућом електронском микроскопијом (СЕМ) док је кристална
структура испитивана рендгенском анализом (ХРД) и Раманском спектроскопијом
Хемијски састав је урађен помоћу спектроскопске фотоемисије X-зрака (ХПС) У овом
раду је испитиван утицај кристалне структуре и морфологије нанотубуларног филма
TiO2 на фотокаталитичку деградацију воденог раствора метил оранжа (МО) под
дејством ултраљубичастог зрачења Наноцеви TiO2 синтероване на 650 degC 30 мин
показују најбољу кристалоичност и фотокаталитичку активност у поређењу са
осталим филмовима TiO2
Кључне речи Титанијум диоксид анодизација синтеровање кристална фаза
фотокатализа
copy 2016 Authors Published by the International Institute for the Science of Sintering This
article is an open access article distributed under the terms and conditions of the Creative
Commons mdash Attribution 40 International license
(httpscreativecommonsorglicensesby40)
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
43
In order to determine the phase composition and crystallinity of TiO2 nanotube arrays
at different sintering temperatures the XRD diffractograms and Raman spectra were studied
Fig 2 shows the diffractograms of TiO2 nanotube arrays annealed at a different temperature
The as-anodized TiO2 nanotubes are amorphous due to which only the peaks of the titanium
substrate are present in the diffractogram With annealing TiO2 nanotubes crystallized in two
polymorphous forms anatase and rutile At 450 degC anatase was observed as the main crystal
phase due to the presence of two main anatase peaks at 253deg and 48deg corresponding to the
(101) and (200) planes respectively Also a small amount of the rutile phase appeared at
273deg (110) All other peaks came from the substrate which dominated due to the low
thickness of the film Mor at al [19] reported that in nanotubes on a titanium substrate rutile
appeared at 430 degC while in nanotubes on conductive glass annealed at 500 degC rutile did not
appear This happened due to the growth of rutile crystallites at the interface between the
nanotube bottom and the thermally oxidized Ti substrate [7] With temperature rise to 600 degC
new peaks appeared at 361deg (101) 414deg (111) 44deg (210) 543deg (211) 567deg (220) and 689deg
(301) which corresponded to the rutile phase With further temperature increase up to 650
and 700 degC the intensity of the rutile peaks gradually strengthened while the intensity of
peaks from anatase decreased proving that almost all anatase transformed into rutile A
decrease of the diffraction intensity of the titanium foil was also observed revealing the
crystallization of the support [20] The phase composition and the crystallite size estimated
using Scherrerʼs formula are shown in Tab II The crystal size of anatase and rutile was
growing until the temperature reached 650 degC when it started to drop probably due to the
collapse of the nanotube structure
Fig 2 XRD patterns of the as-anodized and sintered TiO2 nanotubes (A-anatase R-rutile Ti-
titanium)
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
44
Tab II Phase composition and average crystallite size of annealed TiO2 nanotubes
Temperature
of annealing oC
Amount of
anatase phase
Amount of
rutile phase
Crystallite size
for anatase
(101)
Crystallite size
for rutile
(110)
450 997 03 231 54
600 203 797 289 257
650 25 975 262 346
700 06 994 242 273
The temperature-induced anatase and rutile crystal modifications of TiO2 were
tracked using spectroscopy methods The Raman spectrum of the sample annealed at 450 degC
(Fig 3) showed only the Raman peaks characteristic for the crystal modification of anatase at
145 cm-1 (Eg(1) mode) 198 cm-1 (Eg(2) mode) and 395 cm-1 (B1g(1) mode) as well as the
peak at 515 cm-1 that corresponds to the superposition of the A1g and B1g(2) modes and the
peak at 635 cm-1 which comes from the Eg(3) mode [21-23] With an increase in temperature
new peaks started to appear in the Raman spectra along with anatase peaks At 600 degC the
rutile Eg mode at 425 cm-1 occurred besides the anatase modes Further temperature increase
up to 650 degC resulted in more intensive rutile peaks while the intensity of all the major
anatase modes decreased and only the main anatase mode at 145 cm-1 remained clearly
visible
Fig 3 Raman spectra of annealed TiO2 nanotubes (A-anatase R-rutile)
The rutile phase was observed as the dominant one identified by the Eg mode at 446 cm-
1and A1g mode at 609 cm-1 as well as by the broad peak at 242 cm-1 which originated from
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
45
the second-order vibrational mode Eg (SO) and disorder effects [24 25] At 700 degC the main
anatase mode was replaced with the rutile B1g mode at 142 cm-1 indicating that anatase
phase completely disappeared The whole spectrum at this temperature was assigned to the
rutile phase where the four Raman modes were prominent enough (B1g Eg A1g and Eg (SO))
while the mode expected at 826-827 cm-1 was too weak to be observed
An XPS study was further employed in order to investigate how different annealing
temperatures influenced the chemical composition of anodized titanium foil The results are
presented in Fig 4 In pristine TiO2 titanium (Ti 2p) oxygen (O1s) carbon (C1s) nitrogen
(N1s) fluoride (F1s) and lead (4f) XPS peaks were noticed After a heat treatment peaks of
lead fluoride and nitrogen disappeared proving that they were caused by surface
contamination No significant changes were noticed for the samples annealed at 450 and 600
degC relative to pristine samples Since the positions of Ti 2p32 and Ti 2p12 peaks (Fig 5) in
these samples ranged from 45816 to 45837 eV and from 46385 to 46410 eV respectively
it clearly indicated the existence of a Ti4+ state [26 27] Moreover the difference in the
binding energy of Ti 2p32 and Ti 2p12 peaks in all of the annealed samples was in accordance
with the literature data for the mentioned state of titanium Although at higher annealing
temperatures both peaks shifted slightly towards lower binding energies their positions still
remained well above the binding energy of the Ti3+ state [27 28] In the O1s regions of
binding energy the peak at 5296-5297 eV proved O-Ti4+ bonding (Fig 6) [29] It was
possible to assign it to the lattice oxygen in TiO2 On the other hand the shoulder effect that
could be fitted with the peak at 5310 plusmn 02 eV probably originated from surface-adsorbed
oxygen (within the hydroxyl groups at the outermost surface as well as within the adsorbed
water resulting from moisture adsorption in air) [29] The increase in annealing temperature
up to 650 degC caused the reduction of the surface-adsorbed oxygen content The atomic ratio
OlattTi2p provides an insight into the stoichiometry of the structure
Fig 4 XPS survey spectrum for as-anodized TiO2 and sintered TiO2
The results show the substoichiometric structure for the amorphous (as-anodized) sample
(Tab III) which probably indicates the presence of oxygen vacancies in it It can be assumed
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
46
that after annealing the filling of oxygen defects proceeded which was assisted by the
crystallization process since annealing was taking place in air
Fig 5 XPS spectrum for Ti 2p peak for as-anodized and sintered TiO2
Tab III XPS results of as-anodized and sintered TiO2
Samples OlattOtot
(area )
OadsOtot
(area )
OlattTi2p
(atomic ratio)
BE(Ti2p12)-BE(Ti2p32)
(eV)
As-
anodized
587 413 16 577
450 oC 799 201 21 573
600 oC 820 180 21 572
650 oC 843 157 21 569
700 oC 815 185 21 572
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
47
Fig 6 XPS spectrum for O 1s peak for as-anodized and sintered TiO2
Tab IV Influence of sintering temperature on photocatalytic degradation ndash first-order rate
constant and correlation coefficient
Temperature of
annealing oC
|k| x 10-2
min-1
R2
450 109 096
600 111 098
650 124 094
700 062 090
The influence of the sintering temperature of TiO2 nanotubes on the degradation of the MO
textile dye is shown on Fig 7a A further analysis indicated that the reaction could be
presented as ln(CCo) = ln(AAo) = kt where Co was the initial dye concentration C was the
concentration after irradiation for time t Ao and A were the corresponding absorbance while k
was a rate constant Fig 7b shows the linear curves proving that the degradation of MB by
sintered TiO2 nanotubes follows the pseudo-first order kinetic The first-order constant k and
the correlation coefficient R2 are shown in Tab IV It is evident that an increased annealing
temperature was accompanied by the increase of k up to 700 degC when it began to decrease
gradually The samples sintered at 450 degC and 600 degC had similar morphology parameters but
there was a difference in the crystal structure The reason for a higher kinetic constant for the
sample annealed at 600 degC was probably the presence of the rutile phase The best
photocatalytic activity shows sample annealed at 650 degC due to the optimum ratio of
anataserutile phase The worst photocatalytic performance was exhibited by the sample
annealed at 700 degC and this can be explained by the collapse of the nanotubular morphology
and porosity loss combined with the disappearance of the anatase phase (Fig 2) The
advantages of the mixed anatase-rutile phase could be due to the efficient trapping and
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
48
separation of photogenerated charges at the phase junction or the separation of the charges
across different crystallite phases [30]
Fig 7 Effect of sintered TiO2 nanotubes on the photocatalytic MO degradation (a) and
photocatalytic kinetic behavior of the degradation of MO by sintered TiO2 nanotubes (b)
4 Conclusions
In this study a highly ordered TiO2 nanotube array on a Ti substrate was successfully
fabricated using electrochemical anodization It was observed that the morphologies and
crystallinity of the TiO2 nanotube array were greatly influenced by the sintering temperature
It was shown the sample annealed at 450 degC consisted mostly of the anatase phase while 994
of rutile was formed at 700 degC At the temperatures of 600 degC and 650 degC a mixture of
anatase and rutile was observed Different amounts of the polymorph phase strongly
influenced the photodegradation of the MO dye It was established that the TiO2 nanotube
array sintered at 650 degC showed the best photocatalytic activity due to the optimal anatase-to-
rutile ratio With a further increase in temperature up to 700 degC the photocatalytic activity
drastically decreased due to the collapse of the nanotubular structure and the excessive rutile
content As a result of the presented investigation an appropriate tailoring of the ratio of
polymorph phases in TiO2 nanotubes could lead to a more suitable photocatalyst
Acknowledgements
This research was supported by the project OI 172057 and project III 45019 of the
Ministry of Education Science and Technological Development of the Republic of Serbia
and by NSF CREST (HRD-0833184) NASA (NNX09AV07A) and NSF-PREM1523617
awards The work in Lausanne was supported by grants from Switzerland through the Swiss
Contribution (SH7220) E H wants to thank the AIT grant the Zeno-Karl Schindler
foundation and MBR Global Water Initiatives for their support
5 References
1 X Chen Z Wu D Liu and Z Gao Nanoscale Res Lett 12 1 (2017) 143
2 E Bailoacuten-Garciacutea A Elmouwahidi F Carrasco-Mariacuten A F Peacuterez-Cadenas and F J
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
49
Maldonado-Hoacutedar Appl Catal B Environ 217 (2017) 540-550
3 H Zhang X Chen Z Li J Kou T Yu and Z Zou J Phys D Appl Phys 40 21
(2007) 6846-6849
4 M Sabarinathan S Harish J Archana M Navaneethan H Ikeda and Y
Hayakawa RSC Adv 7 40 (2017) 24754-24763
5 M R Hoffmann S T Martin W Choi and D W Bahnemann Chem Rev 95 1
(1995) 69-96
6 K Nakata and A Fujishima J Photochem Photobiol C Photochem Rev 13 3
(2012) 169-189
7 D Fang Z Luo K Huang and D C Lagoudas Appl Surf Sci 257 15 (2011)
6451-6461
8 J M Macak M Zlamal J Krysa and P Schmuki Small 3 2 (2007) 300-304
9 Y Lai L Sun Y Chen H Zhuang C Lin and J W Chin J Electrochem Soc
153 7 (2006) D123
10 Y Sun K Yan G Wang W Guo and T Ma J Phys Chem C 115 26 (2011)
12844-12849
11 H J Oh J H Lee Y J Kim S J Suh J H Lee and C S Chi Appl Catal B
Environ 84 1ndash2 (2008) 142-147
12 N Masahashi Y Mizukoshi S Semboshi and N Ohtsu Appl Catal B Environ
901ndash2 (2009) 255-261
13 J Zhang Q Xu Z Feng M Li and C Li Angew Chemie Int Ed 47 9 (2008)
1766-1769
14 J Yu and B Wang Appl Catal B Environ 94 3ndash4 (2010) 295-302
15 O Carp C L Huisman and A Reller Prog Solid State Chem 32 1ndash2 (2004) 33-
177
16 B D Cullity Elements of x-ray diffraction Reading MA Addison-Wesley
Publishing Company Inc 1978
17 A G Kontos et al Chem Phys Lett 490 1ndash3 (2010) 58-62
18 Z Su and W Zhou J Mater Chem 21 25 (2011) 8955
19 G K Mor O K Varghese M Paulose K Shankar and C a Grimes Sol Energy
Mater Sol Cells 90 14 (2006) 2011-2075
20 Y Li et al Appl Surf Sci 297 (2014) 103-108
21 T Ohsaka F Izumi and Y Fujiki J Raman Spectrosc 7 6 (1978) 321-324
22 W F Zhang Y L He M S Zhang Z Yin and Q Chen J Phys D Appl Phys
33 8 (2000) 912-916
23 H C Choi Y M Jung and S Bin Kim Vib Spectrosc 37 1 (2005) 33-38
24 Y Hara and M Nicol Phys Status Solidi 94 1 (1979) 317-322
25 B Santara P K Giri K Imakita and M Fujii J Phys D Appl Phys47 21 (2014)
215302
26 Z Lou Y Li H Song Z Ye and L Zhu RSC Adv 6 51 (2016) 45343-45348
27 X Zhu J Chen X Yu X Zhu X Gao and K Cen RSC Adv 5 39 (2015) 30416-
30424
28 Y Fu H Du S Zhang and W Huang Mater Sci Eng A 403 1ndash2 (2005) 25-31
29 Z Fan H Guo K Fang and Y Sun RSC Adv 5 31 (2015) 24795-24802
30 Y K Kho A Iwase W Y Teoh L Madler A Kudo and R Amal J Phys Chem
C 114 6 (2010) 2821-2829
Садржај Једнодимензионе наноцеви TiO2 усправно орјентисане на супстрат добијене
су електрохемијском анодизацијом титанијумске фолије у киселом електролиту У
циљу промене кристалне структуре и морфологије филма анодизовани аморфни
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
50
филмови TiO2 синтеровани су на високој температури Морфолошка промена
посматрана је скенирајућом електронском микроскопијом (СЕМ) док је кристална
структура испитивана рендгенском анализом (ХРД) и Раманском спектроскопијом
Хемијски састав је урађен помоћу спектроскопске фотоемисије X-зрака (ХПС) У овом
раду је испитиван утицај кристалне структуре и морфологије нанотубуларног филма
TiO2 на фотокаталитичку деградацију воденог раствора метил оранжа (МО) под
дејством ултраљубичастог зрачења Наноцеви TiO2 синтероване на 650 degC 30 мин
показују најбољу кристалоичност и фотокаталитичку активност у поређењу са
осталим филмовима TiO2
Кључне речи Титанијум диоксид анодизација синтеровање кристална фаза
фотокатализа
copy 2016 Authors Published by the International Institute for the Science of Sintering This
article is an open access article distributed under the terms and conditions of the Creative
Commons mdash Attribution 40 International license
(httpscreativecommonsorglicensesby40)
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
44
Tab II Phase composition and average crystallite size of annealed TiO2 nanotubes
Temperature
of annealing oC
Amount of
anatase phase
Amount of
rutile phase
Crystallite size
for anatase
(101)
Crystallite size
for rutile
(110)
450 997 03 231 54
600 203 797 289 257
650 25 975 262 346
700 06 994 242 273
The temperature-induced anatase and rutile crystal modifications of TiO2 were
tracked using spectroscopy methods The Raman spectrum of the sample annealed at 450 degC
(Fig 3) showed only the Raman peaks characteristic for the crystal modification of anatase at
145 cm-1 (Eg(1) mode) 198 cm-1 (Eg(2) mode) and 395 cm-1 (B1g(1) mode) as well as the
peak at 515 cm-1 that corresponds to the superposition of the A1g and B1g(2) modes and the
peak at 635 cm-1 which comes from the Eg(3) mode [21-23] With an increase in temperature
new peaks started to appear in the Raman spectra along with anatase peaks At 600 degC the
rutile Eg mode at 425 cm-1 occurred besides the anatase modes Further temperature increase
up to 650 degC resulted in more intensive rutile peaks while the intensity of all the major
anatase modes decreased and only the main anatase mode at 145 cm-1 remained clearly
visible
Fig 3 Raman spectra of annealed TiO2 nanotubes (A-anatase R-rutile)
The rutile phase was observed as the dominant one identified by the Eg mode at 446 cm-
1and A1g mode at 609 cm-1 as well as by the broad peak at 242 cm-1 which originated from
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
45
the second-order vibrational mode Eg (SO) and disorder effects [24 25] At 700 degC the main
anatase mode was replaced with the rutile B1g mode at 142 cm-1 indicating that anatase
phase completely disappeared The whole spectrum at this temperature was assigned to the
rutile phase where the four Raman modes were prominent enough (B1g Eg A1g and Eg (SO))
while the mode expected at 826-827 cm-1 was too weak to be observed
An XPS study was further employed in order to investigate how different annealing
temperatures influenced the chemical composition of anodized titanium foil The results are
presented in Fig 4 In pristine TiO2 titanium (Ti 2p) oxygen (O1s) carbon (C1s) nitrogen
(N1s) fluoride (F1s) and lead (4f) XPS peaks were noticed After a heat treatment peaks of
lead fluoride and nitrogen disappeared proving that they were caused by surface
contamination No significant changes were noticed for the samples annealed at 450 and 600
degC relative to pristine samples Since the positions of Ti 2p32 and Ti 2p12 peaks (Fig 5) in
these samples ranged from 45816 to 45837 eV and from 46385 to 46410 eV respectively
it clearly indicated the existence of a Ti4+ state [26 27] Moreover the difference in the
binding energy of Ti 2p32 and Ti 2p12 peaks in all of the annealed samples was in accordance
with the literature data for the mentioned state of titanium Although at higher annealing
temperatures both peaks shifted slightly towards lower binding energies their positions still
remained well above the binding energy of the Ti3+ state [27 28] In the O1s regions of
binding energy the peak at 5296-5297 eV proved O-Ti4+ bonding (Fig 6) [29] It was
possible to assign it to the lattice oxygen in TiO2 On the other hand the shoulder effect that
could be fitted with the peak at 5310 plusmn 02 eV probably originated from surface-adsorbed
oxygen (within the hydroxyl groups at the outermost surface as well as within the adsorbed
water resulting from moisture adsorption in air) [29] The increase in annealing temperature
up to 650 degC caused the reduction of the surface-adsorbed oxygen content The atomic ratio
OlattTi2p provides an insight into the stoichiometry of the structure
Fig 4 XPS survey spectrum for as-anodized TiO2 and sintered TiO2
The results show the substoichiometric structure for the amorphous (as-anodized) sample
(Tab III) which probably indicates the presence of oxygen vacancies in it It can be assumed
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
46
that after annealing the filling of oxygen defects proceeded which was assisted by the
crystallization process since annealing was taking place in air
Fig 5 XPS spectrum for Ti 2p peak for as-anodized and sintered TiO2
Tab III XPS results of as-anodized and sintered TiO2
Samples OlattOtot
(area )
OadsOtot
(area )
OlattTi2p
(atomic ratio)
BE(Ti2p12)-BE(Ti2p32)
(eV)
As-
anodized
587 413 16 577
450 oC 799 201 21 573
600 oC 820 180 21 572
650 oC 843 157 21 569
700 oC 815 185 21 572
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
47
Fig 6 XPS spectrum for O 1s peak for as-anodized and sintered TiO2
Tab IV Influence of sintering temperature on photocatalytic degradation ndash first-order rate
constant and correlation coefficient
Temperature of
annealing oC
|k| x 10-2
min-1
R2
450 109 096
600 111 098
650 124 094
700 062 090
The influence of the sintering temperature of TiO2 nanotubes on the degradation of the MO
textile dye is shown on Fig 7a A further analysis indicated that the reaction could be
presented as ln(CCo) = ln(AAo) = kt where Co was the initial dye concentration C was the
concentration after irradiation for time t Ao and A were the corresponding absorbance while k
was a rate constant Fig 7b shows the linear curves proving that the degradation of MB by
sintered TiO2 nanotubes follows the pseudo-first order kinetic The first-order constant k and
the correlation coefficient R2 are shown in Tab IV It is evident that an increased annealing
temperature was accompanied by the increase of k up to 700 degC when it began to decrease
gradually The samples sintered at 450 degC and 600 degC had similar morphology parameters but
there was a difference in the crystal structure The reason for a higher kinetic constant for the
sample annealed at 600 degC was probably the presence of the rutile phase The best
photocatalytic activity shows sample annealed at 650 degC due to the optimum ratio of
anataserutile phase The worst photocatalytic performance was exhibited by the sample
annealed at 700 degC and this can be explained by the collapse of the nanotubular morphology
and porosity loss combined with the disappearance of the anatase phase (Fig 2) The
advantages of the mixed anatase-rutile phase could be due to the efficient trapping and
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
48
separation of photogenerated charges at the phase junction or the separation of the charges
across different crystallite phases [30]
Fig 7 Effect of sintered TiO2 nanotubes on the photocatalytic MO degradation (a) and
photocatalytic kinetic behavior of the degradation of MO by sintered TiO2 nanotubes (b)
4 Conclusions
In this study a highly ordered TiO2 nanotube array on a Ti substrate was successfully
fabricated using electrochemical anodization It was observed that the morphologies and
crystallinity of the TiO2 nanotube array were greatly influenced by the sintering temperature
It was shown the sample annealed at 450 degC consisted mostly of the anatase phase while 994
of rutile was formed at 700 degC At the temperatures of 600 degC and 650 degC a mixture of
anatase and rutile was observed Different amounts of the polymorph phase strongly
influenced the photodegradation of the MO dye It was established that the TiO2 nanotube
array sintered at 650 degC showed the best photocatalytic activity due to the optimal anatase-to-
rutile ratio With a further increase in temperature up to 700 degC the photocatalytic activity
drastically decreased due to the collapse of the nanotubular structure and the excessive rutile
content As a result of the presented investigation an appropriate tailoring of the ratio of
polymorph phases in TiO2 nanotubes could lead to a more suitable photocatalyst
Acknowledgements
This research was supported by the project OI 172057 and project III 45019 of the
Ministry of Education Science and Technological Development of the Republic of Serbia
and by NSF CREST (HRD-0833184) NASA (NNX09AV07A) and NSF-PREM1523617
awards The work in Lausanne was supported by grants from Switzerland through the Swiss
Contribution (SH7220) E H wants to thank the AIT grant the Zeno-Karl Schindler
foundation and MBR Global Water Initiatives for their support
5 References
1 X Chen Z Wu D Liu and Z Gao Nanoscale Res Lett 12 1 (2017) 143
2 E Bailoacuten-Garciacutea A Elmouwahidi F Carrasco-Mariacuten A F Peacuterez-Cadenas and F J
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
49
Maldonado-Hoacutedar Appl Catal B Environ 217 (2017) 540-550
3 H Zhang X Chen Z Li J Kou T Yu and Z Zou J Phys D Appl Phys 40 21
(2007) 6846-6849
4 M Sabarinathan S Harish J Archana M Navaneethan H Ikeda and Y
Hayakawa RSC Adv 7 40 (2017) 24754-24763
5 M R Hoffmann S T Martin W Choi and D W Bahnemann Chem Rev 95 1
(1995) 69-96
6 K Nakata and A Fujishima J Photochem Photobiol C Photochem Rev 13 3
(2012) 169-189
7 D Fang Z Luo K Huang and D C Lagoudas Appl Surf Sci 257 15 (2011)
6451-6461
8 J M Macak M Zlamal J Krysa and P Schmuki Small 3 2 (2007) 300-304
9 Y Lai L Sun Y Chen H Zhuang C Lin and J W Chin J Electrochem Soc
153 7 (2006) D123
10 Y Sun K Yan G Wang W Guo and T Ma J Phys Chem C 115 26 (2011)
12844-12849
11 H J Oh J H Lee Y J Kim S J Suh J H Lee and C S Chi Appl Catal B
Environ 84 1ndash2 (2008) 142-147
12 N Masahashi Y Mizukoshi S Semboshi and N Ohtsu Appl Catal B Environ
901ndash2 (2009) 255-261
13 J Zhang Q Xu Z Feng M Li and C Li Angew Chemie Int Ed 47 9 (2008)
1766-1769
14 J Yu and B Wang Appl Catal B Environ 94 3ndash4 (2010) 295-302
15 O Carp C L Huisman and A Reller Prog Solid State Chem 32 1ndash2 (2004) 33-
177
16 B D Cullity Elements of x-ray diffraction Reading MA Addison-Wesley
Publishing Company Inc 1978
17 A G Kontos et al Chem Phys Lett 490 1ndash3 (2010) 58-62
18 Z Su and W Zhou J Mater Chem 21 25 (2011) 8955
19 G K Mor O K Varghese M Paulose K Shankar and C a Grimes Sol Energy
Mater Sol Cells 90 14 (2006) 2011-2075
20 Y Li et al Appl Surf Sci 297 (2014) 103-108
21 T Ohsaka F Izumi and Y Fujiki J Raman Spectrosc 7 6 (1978) 321-324
22 W F Zhang Y L He M S Zhang Z Yin and Q Chen J Phys D Appl Phys
33 8 (2000) 912-916
23 H C Choi Y M Jung and S Bin Kim Vib Spectrosc 37 1 (2005) 33-38
24 Y Hara and M Nicol Phys Status Solidi 94 1 (1979) 317-322
25 B Santara P K Giri K Imakita and M Fujii J Phys D Appl Phys47 21 (2014)
215302
26 Z Lou Y Li H Song Z Ye and L Zhu RSC Adv 6 51 (2016) 45343-45348
27 X Zhu J Chen X Yu X Zhu X Gao and K Cen RSC Adv 5 39 (2015) 30416-
30424
28 Y Fu H Du S Zhang and W Huang Mater Sci Eng A 403 1ndash2 (2005) 25-31
29 Z Fan H Guo K Fang and Y Sun RSC Adv 5 31 (2015) 24795-24802
30 Y K Kho A Iwase W Y Teoh L Madler A Kudo and R Amal J Phys Chem
C 114 6 (2010) 2821-2829
Садржај Једнодимензионе наноцеви TiO2 усправно орјентисане на супстрат добијене
су електрохемијском анодизацијом титанијумске фолије у киселом електролиту У
циљу промене кристалне структуре и морфологије филма анодизовани аморфни
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
50
филмови TiO2 синтеровани су на високој температури Морфолошка промена
посматрана је скенирајућом електронском микроскопијом (СЕМ) док је кристална
структура испитивана рендгенском анализом (ХРД) и Раманском спектроскопијом
Хемијски састав је урађен помоћу спектроскопске фотоемисије X-зрака (ХПС) У овом
раду је испитиван утицај кристалне структуре и морфологије нанотубуларног филма
TiO2 на фотокаталитичку деградацију воденог раствора метил оранжа (МО) под
дејством ултраљубичастог зрачења Наноцеви TiO2 синтероване на 650 degC 30 мин
показују најбољу кристалоичност и фотокаталитичку активност у поређењу са
осталим филмовима TiO2
Кључне речи Титанијум диоксид анодизација синтеровање кристална фаза
фотокатализа
copy 2016 Authors Published by the International Institute for the Science of Sintering This
article is an open access article distributed under the terms and conditions of the Creative
Commons mdash Attribution 40 International license
(httpscreativecommonsorglicensesby40)
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
45
the second-order vibrational mode Eg (SO) and disorder effects [24 25] At 700 degC the main
anatase mode was replaced with the rutile B1g mode at 142 cm-1 indicating that anatase
phase completely disappeared The whole spectrum at this temperature was assigned to the
rutile phase where the four Raman modes were prominent enough (B1g Eg A1g and Eg (SO))
while the mode expected at 826-827 cm-1 was too weak to be observed
An XPS study was further employed in order to investigate how different annealing
temperatures influenced the chemical composition of anodized titanium foil The results are
presented in Fig 4 In pristine TiO2 titanium (Ti 2p) oxygen (O1s) carbon (C1s) nitrogen
(N1s) fluoride (F1s) and lead (4f) XPS peaks were noticed After a heat treatment peaks of
lead fluoride and nitrogen disappeared proving that they were caused by surface
contamination No significant changes were noticed for the samples annealed at 450 and 600
degC relative to pristine samples Since the positions of Ti 2p32 and Ti 2p12 peaks (Fig 5) in
these samples ranged from 45816 to 45837 eV and from 46385 to 46410 eV respectively
it clearly indicated the existence of a Ti4+ state [26 27] Moreover the difference in the
binding energy of Ti 2p32 and Ti 2p12 peaks in all of the annealed samples was in accordance
with the literature data for the mentioned state of titanium Although at higher annealing
temperatures both peaks shifted slightly towards lower binding energies their positions still
remained well above the binding energy of the Ti3+ state [27 28] In the O1s regions of
binding energy the peak at 5296-5297 eV proved O-Ti4+ bonding (Fig 6) [29] It was
possible to assign it to the lattice oxygen in TiO2 On the other hand the shoulder effect that
could be fitted with the peak at 5310 plusmn 02 eV probably originated from surface-adsorbed
oxygen (within the hydroxyl groups at the outermost surface as well as within the adsorbed
water resulting from moisture adsorption in air) [29] The increase in annealing temperature
up to 650 degC caused the reduction of the surface-adsorbed oxygen content The atomic ratio
OlattTi2p provides an insight into the stoichiometry of the structure
Fig 4 XPS survey spectrum for as-anodized TiO2 and sintered TiO2
The results show the substoichiometric structure for the amorphous (as-anodized) sample
(Tab III) which probably indicates the presence of oxygen vacancies in it It can be assumed
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
46
that after annealing the filling of oxygen defects proceeded which was assisted by the
crystallization process since annealing was taking place in air
Fig 5 XPS spectrum for Ti 2p peak for as-anodized and sintered TiO2
Tab III XPS results of as-anodized and sintered TiO2
Samples OlattOtot
(area )
OadsOtot
(area )
OlattTi2p
(atomic ratio)
BE(Ti2p12)-BE(Ti2p32)
(eV)
As-
anodized
587 413 16 577
450 oC 799 201 21 573
600 oC 820 180 21 572
650 oC 843 157 21 569
700 oC 815 185 21 572
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
47
Fig 6 XPS spectrum for O 1s peak for as-anodized and sintered TiO2
Tab IV Influence of sintering temperature on photocatalytic degradation ndash first-order rate
constant and correlation coefficient
Temperature of
annealing oC
|k| x 10-2
min-1
R2
450 109 096
600 111 098
650 124 094
700 062 090
The influence of the sintering temperature of TiO2 nanotubes on the degradation of the MO
textile dye is shown on Fig 7a A further analysis indicated that the reaction could be
presented as ln(CCo) = ln(AAo) = kt where Co was the initial dye concentration C was the
concentration after irradiation for time t Ao and A were the corresponding absorbance while k
was a rate constant Fig 7b shows the linear curves proving that the degradation of MB by
sintered TiO2 nanotubes follows the pseudo-first order kinetic The first-order constant k and
the correlation coefficient R2 are shown in Tab IV It is evident that an increased annealing
temperature was accompanied by the increase of k up to 700 degC when it began to decrease
gradually The samples sintered at 450 degC and 600 degC had similar morphology parameters but
there was a difference in the crystal structure The reason for a higher kinetic constant for the
sample annealed at 600 degC was probably the presence of the rutile phase The best
photocatalytic activity shows sample annealed at 650 degC due to the optimum ratio of
anataserutile phase The worst photocatalytic performance was exhibited by the sample
annealed at 700 degC and this can be explained by the collapse of the nanotubular morphology
and porosity loss combined with the disappearance of the anatase phase (Fig 2) The
advantages of the mixed anatase-rutile phase could be due to the efficient trapping and
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
48
separation of photogenerated charges at the phase junction or the separation of the charges
across different crystallite phases [30]
Fig 7 Effect of sintered TiO2 nanotubes on the photocatalytic MO degradation (a) and
photocatalytic kinetic behavior of the degradation of MO by sintered TiO2 nanotubes (b)
4 Conclusions
In this study a highly ordered TiO2 nanotube array on a Ti substrate was successfully
fabricated using electrochemical anodization It was observed that the morphologies and
crystallinity of the TiO2 nanotube array were greatly influenced by the sintering temperature
It was shown the sample annealed at 450 degC consisted mostly of the anatase phase while 994
of rutile was formed at 700 degC At the temperatures of 600 degC and 650 degC a mixture of
anatase and rutile was observed Different amounts of the polymorph phase strongly
influenced the photodegradation of the MO dye It was established that the TiO2 nanotube
array sintered at 650 degC showed the best photocatalytic activity due to the optimal anatase-to-
rutile ratio With a further increase in temperature up to 700 degC the photocatalytic activity
drastically decreased due to the collapse of the nanotubular structure and the excessive rutile
content As a result of the presented investigation an appropriate tailoring of the ratio of
polymorph phases in TiO2 nanotubes could lead to a more suitable photocatalyst
Acknowledgements
This research was supported by the project OI 172057 and project III 45019 of the
Ministry of Education Science and Technological Development of the Republic of Serbia
and by NSF CREST (HRD-0833184) NASA (NNX09AV07A) and NSF-PREM1523617
awards The work in Lausanne was supported by grants from Switzerland through the Swiss
Contribution (SH7220) E H wants to thank the AIT grant the Zeno-Karl Schindler
foundation and MBR Global Water Initiatives for their support
5 References
1 X Chen Z Wu D Liu and Z Gao Nanoscale Res Lett 12 1 (2017) 143
2 E Bailoacuten-Garciacutea A Elmouwahidi F Carrasco-Mariacuten A F Peacuterez-Cadenas and F J
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
49
Maldonado-Hoacutedar Appl Catal B Environ 217 (2017) 540-550
3 H Zhang X Chen Z Li J Kou T Yu and Z Zou J Phys D Appl Phys 40 21
(2007) 6846-6849
4 M Sabarinathan S Harish J Archana M Navaneethan H Ikeda and Y
Hayakawa RSC Adv 7 40 (2017) 24754-24763
5 M R Hoffmann S T Martin W Choi and D W Bahnemann Chem Rev 95 1
(1995) 69-96
6 K Nakata and A Fujishima J Photochem Photobiol C Photochem Rev 13 3
(2012) 169-189
7 D Fang Z Luo K Huang and D C Lagoudas Appl Surf Sci 257 15 (2011)
6451-6461
8 J M Macak M Zlamal J Krysa and P Schmuki Small 3 2 (2007) 300-304
9 Y Lai L Sun Y Chen H Zhuang C Lin and J W Chin J Electrochem Soc
153 7 (2006) D123
10 Y Sun K Yan G Wang W Guo and T Ma J Phys Chem C 115 26 (2011)
12844-12849
11 H J Oh J H Lee Y J Kim S J Suh J H Lee and C S Chi Appl Catal B
Environ 84 1ndash2 (2008) 142-147
12 N Masahashi Y Mizukoshi S Semboshi and N Ohtsu Appl Catal B Environ
901ndash2 (2009) 255-261
13 J Zhang Q Xu Z Feng M Li and C Li Angew Chemie Int Ed 47 9 (2008)
1766-1769
14 J Yu and B Wang Appl Catal B Environ 94 3ndash4 (2010) 295-302
15 O Carp C L Huisman and A Reller Prog Solid State Chem 32 1ndash2 (2004) 33-
177
16 B D Cullity Elements of x-ray diffraction Reading MA Addison-Wesley
Publishing Company Inc 1978
17 A G Kontos et al Chem Phys Lett 490 1ndash3 (2010) 58-62
18 Z Su and W Zhou J Mater Chem 21 25 (2011) 8955
19 G K Mor O K Varghese M Paulose K Shankar and C a Grimes Sol Energy
Mater Sol Cells 90 14 (2006) 2011-2075
20 Y Li et al Appl Surf Sci 297 (2014) 103-108
21 T Ohsaka F Izumi and Y Fujiki J Raman Spectrosc 7 6 (1978) 321-324
22 W F Zhang Y L He M S Zhang Z Yin and Q Chen J Phys D Appl Phys
33 8 (2000) 912-916
23 H C Choi Y M Jung and S Bin Kim Vib Spectrosc 37 1 (2005) 33-38
24 Y Hara and M Nicol Phys Status Solidi 94 1 (1979) 317-322
25 B Santara P K Giri K Imakita and M Fujii J Phys D Appl Phys47 21 (2014)
215302
26 Z Lou Y Li H Song Z Ye and L Zhu RSC Adv 6 51 (2016) 45343-45348
27 X Zhu J Chen X Yu X Zhu X Gao and K Cen RSC Adv 5 39 (2015) 30416-
30424
28 Y Fu H Du S Zhang and W Huang Mater Sci Eng A 403 1ndash2 (2005) 25-31
29 Z Fan H Guo K Fang and Y Sun RSC Adv 5 31 (2015) 24795-24802
30 Y K Kho A Iwase W Y Teoh L Madler A Kudo and R Amal J Phys Chem
C 114 6 (2010) 2821-2829
Садржај Једнодимензионе наноцеви TiO2 усправно орјентисане на супстрат добијене
су електрохемијском анодизацијом титанијумске фолије у киселом електролиту У
циљу промене кристалне структуре и морфологије филма анодизовани аморфни
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
50
филмови TiO2 синтеровани су на високој температури Морфолошка промена
посматрана је скенирајућом електронском микроскопијом (СЕМ) док је кристална
структура испитивана рендгенском анализом (ХРД) и Раманском спектроскопијом
Хемијски састав је урађен помоћу спектроскопске фотоемисије X-зрака (ХПС) У овом
раду је испитиван утицај кристалне структуре и морфологије нанотубуларног филма
TiO2 на фотокаталитичку деградацију воденог раствора метил оранжа (МО) под
дејством ултраљубичастог зрачења Наноцеви TiO2 синтероване на 650 degC 30 мин
показују најбољу кристалоичност и фотокаталитичку активност у поређењу са
осталим филмовима TiO2
Кључне речи Титанијум диоксид анодизација синтеровање кристална фаза
фотокатализа
copy 2016 Authors Published by the International Institute for the Science of Sintering This
article is an open access article distributed under the terms and conditions of the Creative
Commons mdash Attribution 40 International license
(httpscreativecommonsorglicensesby40)
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
46
that after annealing the filling of oxygen defects proceeded which was assisted by the
crystallization process since annealing was taking place in air
Fig 5 XPS spectrum for Ti 2p peak for as-anodized and sintered TiO2
Tab III XPS results of as-anodized and sintered TiO2
Samples OlattOtot
(area )
OadsOtot
(area )
OlattTi2p
(atomic ratio)
BE(Ti2p12)-BE(Ti2p32)
(eV)
As-
anodized
587 413 16 577
450 oC 799 201 21 573
600 oC 820 180 21 572
650 oC 843 157 21 569
700 oC 815 185 21 572
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
47
Fig 6 XPS spectrum for O 1s peak for as-anodized and sintered TiO2
Tab IV Influence of sintering temperature on photocatalytic degradation ndash first-order rate
constant and correlation coefficient
Temperature of
annealing oC
|k| x 10-2
min-1
R2
450 109 096
600 111 098
650 124 094
700 062 090
The influence of the sintering temperature of TiO2 nanotubes on the degradation of the MO
textile dye is shown on Fig 7a A further analysis indicated that the reaction could be
presented as ln(CCo) = ln(AAo) = kt where Co was the initial dye concentration C was the
concentration after irradiation for time t Ao and A were the corresponding absorbance while k
was a rate constant Fig 7b shows the linear curves proving that the degradation of MB by
sintered TiO2 nanotubes follows the pseudo-first order kinetic The first-order constant k and
the correlation coefficient R2 are shown in Tab IV It is evident that an increased annealing
temperature was accompanied by the increase of k up to 700 degC when it began to decrease
gradually The samples sintered at 450 degC and 600 degC had similar morphology parameters but
there was a difference in the crystal structure The reason for a higher kinetic constant for the
sample annealed at 600 degC was probably the presence of the rutile phase The best
photocatalytic activity shows sample annealed at 650 degC due to the optimum ratio of
anataserutile phase The worst photocatalytic performance was exhibited by the sample
annealed at 700 degC and this can be explained by the collapse of the nanotubular morphology
and porosity loss combined with the disappearance of the anatase phase (Fig 2) The
advantages of the mixed anatase-rutile phase could be due to the efficient trapping and
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
48
separation of photogenerated charges at the phase junction or the separation of the charges
across different crystallite phases [30]
Fig 7 Effect of sintered TiO2 nanotubes on the photocatalytic MO degradation (a) and
photocatalytic kinetic behavior of the degradation of MO by sintered TiO2 nanotubes (b)
4 Conclusions
In this study a highly ordered TiO2 nanotube array on a Ti substrate was successfully
fabricated using electrochemical anodization It was observed that the morphologies and
crystallinity of the TiO2 nanotube array were greatly influenced by the sintering temperature
It was shown the sample annealed at 450 degC consisted mostly of the anatase phase while 994
of rutile was formed at 700 degC At the temperatures of 600 degC and 650 degC a mixture of
anatase and rutile was observed Different amounts of the polymorph phase strongly
influenced the photodegradation of the MO dye It was established that the TiO2 nanotube
array sintered at 650 degC showed the best photocatalytic activity due to the optimal anatase-to-
rutile ratio With a further increase in temperature up to 700 degC the photocatalytic activity
drastically decreased due to the collapse of the nanotubular structure and the excessive rutile
content As a result of the presented investigation an appropriate tailoring of the ratio of
polymorph phases in TiO2 nanotubes could lead to a more suitable photocatalyst
Acknowledgements
This research was supported by the project OI 172057 and project III 45019 of the
Ministry of Education Science and Technological Development of the Republic of Serbia
and by NSF CREST (HRD-0833184) NASA (NNX09AV07A) and NSF-PREM1523617
awards The work in Lausanne was supported by grants from Switzerland through the Swiss
Contribution (SH7220) E H wants to thank the AIT grant the Zeno-Karl Schindler
foundation and MBR Global Water Initiatives for their support
5 References
1 X Chen Z Wu D Liu and Z Gao Nanoscale Res Lett 12 1 (2017) 143
2 E Bailoacuten-Garciacutea A Elmouwahidi F Carrasco-Mariacuten A F Peacuterez-Cadenas and F J
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
49
Maldonado-Hoacutedar Appl Catal B Environ 217 (2017) 540-550
3 H Zhang X Chen Z Li J Kou T Yu and Z Zou J Phys D Appl Phys 40 21
(2007) 6846-6849
4 M Sabarinathan S Harish J Archana M Navaneethan H Ikeda and Y
Hayakawa RSC Adv 7 40 (2017) 24754-24763
5 M R Hoffmann S T Martin W Choi and D W Bahnemann Chem Rev 95 1
(1995) 69-96
6 K Nakata and A Fujishima J Photochem Photobiol C Photochem Rev 13 3
(2012) 169-189
7 D Fang Z Luo K Huang and D C Lagoudas Appl Surf Sci 257 15 (2011)
6451-6461
8 J M Macak M Zlamal J Krysa and P Schmuki Small 3 2 (2007) 300-304
9 Y Lai L Sun Y Chen H Zhuang C Lin and J W Chin J Electrochem Soc
153 7 (2006) D123
10 Y Sun K Yan G Wang W Guo and T Ma J Phys Chem C 115 26 (2011)
12844-12849
11 H J Oh J H Lee Y J Kim S J Suh J H Lee and C S Chi Appl Catal B
Environ 84 1ndash2 (2008) 142-147
12 N Masahashi Y Mizukoshi S Semboshi and N Ohtsu Appl Catal B Environ
901ndash2 (2009) 255-261
13 J Zhang Q Xu Z Feng M Li and C Li Angew Chemie Int Ed 47 9 (2008)
1766-1769
14 J Yu and B Wang Appl Catal B Environ 94 3ndash4 (2010) 295-302
15 O Carp C L Huisman and A Reller Prog Solid State Chem 32 1ndash2 (2004) 33-
177
16 B D Cullity Elements of x-ray diffraction Reading MA Addison-Wesley
Publishing Company Inc 1978
17 A G Kontos et al Chem Phys Lett 490 1ndash3 (2010) 58-62
18 Z Su and W Zhou J Mater Chem 21 25 (2011) 8955
19 G K Mor O K Varghese M Paulose K Shankar and C a Grimes Sol Energy
Mater Sol Cells 90 14 (2006) 2011-2075
20 Y Li et al Appl Surf Sci 297 (2014) 103-108
21 T Ohsaka F Izumi and Y Fujiki J Raman Spectrosc 7 6 (1978) 321-324
22 W F Zhang Y L He M S Zhang Z Yin and Q Chen J Phys D Appl Phys
33 8 (2000) 912-916
23 H C Choi Y M Jung and S Bin Kim Vib Spectrosc 37 1 (2005) 33-38
24 Y Hara and M Nicol Phys Status Solidi 94 1 (1979) 317-322
25 B Santara P K Giri K Imakita and M Fujii J Phys D Appl Phys47 21 (2014)
215302
26 Z Lou Y Li H Song Z Ye and L Zhu RSC Adv 6 51 (2016) 45343-45348
27 X Zhu J Chen X Yu X Zhu X Gao and K Cen RSC Adv 5 39 (2015) 30416-
30424
28 Y Fu H Du S Zhang and W Huang Mater Sci Eng A 403 1ndash2 (2005) 25-31
29 Z Fan H Guo K Fang and Y Sun RSC Adv 5 31 (2015) 24795-24802
30 Y K Kho A Iwase W Y Teoh L Madler A Kudo and R Amal J Phys Chem
C 114 6 (2010) 2821-2829
Садржај Једнодимензионе наноцеви TiO2 усправно орјентисане на супстрат добијене
су електрохемијском анодизацијом титанијумске фолије у киселом електролиту У
циљу промене кристалне структуре и морфологије филма анодизовани аморфни
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
50
филмови TiO2 синтеровани су на високој температури Морфолошка промена
посматрана је скенирајућом електронском микроскопијом (СЕМ) док је кристална
структура испитивана рендгенском анализом (ХРД) и Раманском спектроскопијом
Хемијски састав је урађен помоћу спектроскопске фотоемисије X-зрака (ХПС) У овом
раду је испитиван утицај кристалне структуре и морфологије нанотубуларног филма
TiO2 на фотокаталитичку деградацију воденог раствора метил оранжа (МО) под
дејством ултраљубичастог зрачења Наноцеви TiO2 синтероване на 650 degC 30 мин
показују најбољу кристалоичност и фотокаталитичку активност у поређењу са
осталим филмовима TiO2
Кључне речи Титанијум диоксид анодизација синтеровање кристална фаза
фотокатализа
copy 2016 Authors Published by the International Institute for the Science of Sintering This
article is an open access article distributed under the terms and conditions of the Creative
Commons mdash Attribution 40 International license
(httpscreativecommonsorglicensesby40)
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
47
Fig 6 XPS spectrum for O 1s peak for as-anodized and sintered TiO2
Tab IV Influence of sintering temperature on photocatalytic degradation ndash first-order rate
constant and correlation coefficient
Temperature of
annealing oC
|k| x 10-2
min-1
R2
450 109 096
600 111 098
650 124 094
700 062 090
The influence of the sintering temperature of TiO2 nanotubes on the degradation of the MO
textile dye is shown on Fig 7a A further analysis indicated that the reaction could be
presented as ln(CCo) = ln(AAo) = kt where Co was the initial dye concentration C was the
concentration after irradiation for time t Ao and A were the corresponding absorbance while k
was a rate constant Fig 7b shows the linear curves proving that the degradation of MB by
sintered TiO2 nanotubes follows the pseudo-first order kinetic The first-order constant k and
the correlation coefficient R2 are shown in Tab IV It is evident that an increased annealing
temperature was accompanied by the increase of k up to 700 degC when it began to decrease
gradually The samples sintered at 450 degC and 600 degC had similar morphology parameters but
there was a difference in the crystal structure The reason for a higher kinetic constant for the
sample annealed at 600 degC was probably the presence of the rutile phase The best
photocatalytic activity shows sample annealed at 650 degC due to the optimum ratio of
anataserutile phase The worst photocatalytic performance was exhibited by the sample
annealed at 700 degC and this can be explained by the collapse of the nanotubular morphology
and porosity loss combined with the disappearance of the anatase phase (Fig 2) The
advantages of the mixed anatase-rutile phase could be due to the efficient trapping and
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
48
separation of photogenerated charges at the phase junction or the separation of the charges
across different crystallite phases [30]
Fig 7 Effect of sintered TiO2 nanotubes on the photocatalytic MO degradation (a) and
photocatalytic kinetic behavior of the degradation of MO by sintered TiO2 nanotubes (b)
4 Conclusions
In this study a highly ordered TiO2 nanotube array on a Ti substrate was successfully
fabricated using electrochemical anodization It was observed that the morphologies and
crystallinity of the TiO2 nanotube array were greatly influenced by the sintering temperature
It was shown the sample annealed at 450 degC consisted mostly of the anatase phase while 994
of rutile was formed at 700 degC At the temperatures of 600 degC and 650 degC a mixture of
anatase and rutile was observed Different amounts of the polymorph phase strongly
influenced the photodegradation of the MO dye It was established that the TiO2 nanotube
array sintered at 650 degC showed the best photocatalytic activity due to the optimal anatase-to-
rutile ratio With a further increase in temperature up to 700 degC the photocatalytic activity
drastically decreased due to the collapse of the nanotubular structure and the excessive rutile
content As a result of the presented investigation an appropriate tailoring of the ratio of
polymorph phases in TiO2 nanotubes could lead to a more suitable photocatalyst
Acknowledgements
This research was supported by the project OI 172057 and project III 45019 of the
Ministry of Education Science and Technological Development of the Republic of Serbia
and by NSF CREST (HRD-0833184) NASA (NNX09AV07A) and NSF-PREM1523617
awards The work in Lausanne was supported by grants from Switzerland through the Swiss
Contribution (SH7220) E H wants to thank the AIT grant the Zeno-Karl Schindler
foundation and MBR Global Water Initiatives for their support
5 References
1 X Chen Z Wu D Liu and Z Gao Nanoscale Res Lett 12 1 (2017) 143
2 E Bailoacuten-Garciacutea A Elmouwahidi F Carrasco-Mariacuten A F Peacuterez-Cadenas and F J
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
49
Maldonado-Hoacutedar Appl Catal B Environ 217 (2017) 540-550
3 H Zhang X Chen Z Li J Kou T Yu and Z Zou J Phys D Appl Phys 40 21
(2007) 6846-6849
4 M Sabarinathan S Harish J Archana M Navaneethan H Ikeda and Y
Hayakawa RSC Adv 7 40 (2017) 24754-24763
5 M R Hoffmann S T Martin W Choi and D W Bahnemann Chem Rev 95 1
(1995) 69-96
6 K Nakata and A Fujishima J Photochem Photobiol C Photochem Rev 13 3
(2012) 169-189
7 D Fang Z Luo K Huang and D C Lagoudas Appl Surf Sci 257 15 (2011)
6451-6461
8 J M Macak M Zlamal J Krysa and P Schmuki Small 3 2 (2007) 300-304
9 Y Lai L Sun Y Chen H Zhuang C Lin and J W Chin J Electrochem Soc
153 7 (2006) D123
10 Y Sun K Yan G Wang W Guo and T Ma J Phys Chem C 115 26 (2011)
12844-12849
11 H J Oh J H Lee Y J Kim S J Suh J H Lee and C S Chi Appl Catal B
Environ 84 1ndash2 (2008) 142-147
12 N Masahashi Y Mizukoshi S Semboshi and N Ohtsu Appl Catal B Environ
901ndash2 (2009) 255-261
13 J Zhang Q Xu Z Feng M Li and C Li Angew Chemie Int Ed 47 9 (2008)
1766-1769
14 J Yu and B Wang Appl Catal B Environ 94 3ndash4 (2010) 295-302
15 O Carp C L Huisman and A Reller Prog Solid State Chem 32 1ndash2 (2004) 33-
177
16 B D Cullity Elements of x-ray diffraction Reading MA Addison-Wesley
Publishing Company Inc 1978
17 A G Kontos et al Chem Phys Lett 490 1ndash3 (2010) 58-62
18 Z Su and W Zhou J Mater Chem 21 25 (2011) 8955
19 G K Mor O K Varghese M Paulose K Shankar and C a Grimes Sol Energy
Mater Sol Cells 90 14 (2006) 2011-2075
20 Y Li et al Appl Surf Sci 297 (2014) 103-108
21 T Ohsaka F Izumi and Y Fujiki J Raman Spectrosc 7 6 (1978) 321-324
22 W F Zhang Y L He M S Zhang Z Yin and Q Chen J Phys D Appl Phys
33 8 (2000) 912-916
23 H C Choi Y M Jung and S Bin Kim Vib Spectrosc 37 1 (2005) 33-38
24 Y Hara and M Nicol Phys Status Solidi 94 1 (1979) 317-322
25 B Santara P K Giri K Imakita and M Fujii J Phys D Appl Phys47 21 (2014)
215302
26 Z Lou Y Li H Song Z Ye and L Zhu RSC Adv 6 51 (2016) 45343-45348
27 X Zhu J Chen X Yu X Zhu X Gao and K Cen RSC Adv 5 39 (2015) 30416-
30424
28 Y Fu H Du S Zhang and W Huang Mater Sci Eng A 403 1ndash2 (2005) 25-31
29 Z Fan H Guo K Fang and Y Sun RSC Adv 5 31 (2015) 24795-24802
30 Y K Kho A Iwase W Y Teoh L Madler A Kudo and R Amal J Phys Chem
C 114 6 (2010) 2821-2829
Садржај Једнодимензионе наноцеви TiO2 усправно орјентисане на супстрат добијене
су електрохемијском анодизацијом титанијумске фолије у киселом електролиту У
циљу промене кристалне структуре и морфологије филма анодизовани аморфни
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
50
филмови TiO2 синтеровани су на високој температури Морфолошка промена
посматрана је скенирајућом електронском микроскопијом (СЕМ) док је кристална
структура испитивана рендгенском анализом (ХРД) и Раманском спектроскопијом
Хемијски састав је урађен помоћу спектроскопске фотоемисије X-зрака (ХПС) У овом
раду је испитиван утицај кристалне структуре и морфологије нанотубуларног филма
TiO2 на фотокаталитичку деградацију воденог раствора метил оранжа (МО) под
дејством ултраљубичастог зрачења Наноцеви TiO2 синтероване на 650 degC 30 мин
показују најбољу кристалоичност и фотокаталитичку активност у поређењу са
осталим филмовима TiO2
Кључне речи Титанијум диоксид анодизација синтеровање кристална фаза
фотокатализа
copy 2016 Authors Published by the International Institute for the Science of Sintering This
article is an open access article distributed under the terms and conditions of the Creative
Commons mdash Attribution 40 International license
(httpscreativecommonsorglicensesby40)
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
48
separation of photogenerated charges at the phase junction or the separation of the charges
across different crystallite phases [30]
Fig 7 Effect of sintered TiO2 nanotubes on the photocatalytic MO degradation (a) and
photocatalytic kinetic behavior of the degradation of MO by sintered TiO2 nanotubes (b)
4 Conclusions
In this study a highly ordered TiO2 nanotube array on a Ti substrate was successfully
fabricated using electrochemical anodization It was observed that the morphologies and
crystallinity of the TiO2 nanotube array were greatly influenced by the sintering temperature
It was shown the sample annealed at 450 degC consisted mostly of the anatase phase while 994
of rutile was formed at 700 degC At the temperatures of 600 degC and 650 degC a mixture of
anatase and rutile was observed Different amounts of the polymorph phase strongly
influenced the photodegradation of the MO dye It was established that the TiO2 nanotube
array sintered at 650 degC showed the best photocatalytic activity due to the optimal anatase-to-
rutile ratio With a further increase in temperature up to 700 degC the photocatalytic activity
drastically decreased due to the collapse of the nanotubular structure and the excessive rutile
content As a result of the presented investigation an appropriate tailoring of the ratio of
polymorph phases in TiO2 nanotubes could lead to a more suitable photocatalyst
Acknowledgements
This research was supported by the project OI 172057 and project III 45019 of the
Ministry of Education Science and Technological Development of the Republic of Serbia
and by NSF CREST (HRD-0833184) NASA (NNX09AV07A) and NSF-PREM1523617
awards The work in Lausanne was supported by grants from Switzerland through the Swiss
Contribution (SH7220) E H wants to thank the AIT grant the Zeno-Karl Schindler
foundation and MBR Global Water Initiatives for their support
5 References
1 X Chen Z Wu D Liu and Z Gao Nanoscale Res Lett 12 1 (2017) 143
2 E Bailoacuten-Garciacutea A Elmouwahidi F Carrasco-Mariacuten A F Peacuterez-Cadenas and F J
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
49
Maldonado-Hoacutedar Appl Catal B Environ 217 (2017) 540-550
3 H Zhang X Chen Z Li J Kou T Yu and Z Zou J Phys D Appl Phys 40 21
(2007) 6846-6849
4 M Sabarinathan S Harish J Archana M Navaneethan H Ikeda and Y
Hayakawa RSC Adv 7 40 (2017) 24754-24763
5 M R Hoffmann S T Martin W Choi and D W Bahnemann Chem Rev 95 1
(1995) 69-96
6 K Nakata and A Fujishima J Photochem Photobiol C Photochem Rev 13 3
(2012) 169-189
7 D Fang Z Luo K Huang and D C Lagoudas Appl Surf Sci 257 15 (2011)
6451-6461
8 J M Macak M Zlamal J Krysa and P Schmuki Small 3 2 (2007) 300-304
9 Y Lai L Sun Y Chen H Zhuang C Lin and J W Chin J Electrochem Soc
153 7 (2006) D123
10 Y Sun K Yan G Wang W Guo and T Ma J Phys Chem C 115 26 (2011)
12844-12849
11 H J Oh J H Lee Y J Kim S J Suh J H Lee and C S Chi Appl Catal B
Environ 84 1ndash2 (2008) 142-147
12 N Masahashi Y Mizukoshi S Semboshi and N Ohtsu Appl Catal B Environ
901ndash2 (2009) 255-261
13 J Zhang Q Xu Z Feng M Li and C Li Angew Chemie Int Ed 47 9 (2008)
1766-1769
14 J Yu and B Wang Appl Catal B Environ 94 3ndash4 (2010) 295-302
15 O Carp C L Huisman and A Reller Prog Solid State Chem 32 1ndash2 (2004) 33-
177
16 B D Cullity Elements of x-ray diffraction Reading MA Addison-Wesley
Publishing Company Inc 1978
17 A G Kontos et al Chem Phys Lett 490 1ndash3 (2010) 58-62
18 Z Su and W Zhou J Mater Chem 21 25 (2011) 8955
19 G K Mor O K Varghese M Paulose K Shankar and C a Grimes Sol Energy
Mater Sol Cells 90 14 (2006) 2011-2075
20 Y Li et al Appl Surf Sci 297 (2014) 103-108
21 T Ohsaka F Izumi and Y Fujiki J Raman Spectrosc 7 6 (1978) 321-324
22 W F Zhang Y L He M S Zhang Z Yin and Q Chen J Phys D Appl Phys
33 8 (2000) 912-916
23 H C Choi Y M Jung and S Bin Kim Vib Spectrosc 37 1 (2005) 33-38
24 Y Hara and M Nicol Phys Status Solidi 94 1 (1979) 317-322
25 B Santara P K Giri K Imakita and M Fujii J Phys D Appl Phys47 21 (2014)
215302
26 Z Lou Y Li H Song Z Ye and L Zhu RSC Adv 6 51 (2016) 45343-45348
27 X Zhu J Chen X Yu X Zhu X Gao and K Cen RSC Adv 5 39 (2015) 30416-
30424
28 Y Fu H Du S Zhang and W Huang Mater Sci Eng A 403 1ndash2 (2005) 25-31
29 Z Fan H Guo K Fang and Y Sun RSC Adv 5 31 (2015) 24795-24802
30 Y K Kho A Iwase W Y Teoh L Madler A Kudo and R Amal J Phys Chem
C 114 6 (2010) 2821-2829
Садржај Једнодимензионе наноцеви TiO2 усправно орјентисане на супстрат добијене
су електрохемијском анодизацијом титанијумске фолије у киселом електролиту У
циљу промене кристалне структуре и морфологије филма анодизовани аморфни
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
50
филмови TiO2 синтеровани су на високој температури Морфолошка промена
посматрана је скенирајућом електронском микроскопијом (СЕМ) док је кристална
структура испитивана рендгенском анализом (ХРД) и Раманском спектроскопијом
Хемијски састав је урађен помоћу спектроскопске фотоемисије X-зрака (ХПС) У овом
раду је испитиван утицај кристалне структуре и морфологије нанотубуларног филма
TiO2 на фотокаталитичку деградацију воденог раствора метил оранжа (МО) под
дејством ултраљубичастог зрачења Наноцеви TiO2 синтероване на 650 degC 30 мин
показују најбољу кристалоичност и фотокаталитичку активност у поређењу са
осталим филмовима TiO2
Кључне речи Титанијум диоксид анодизација синтеровање кристална фаза
фотокатализа
copy 2016 Authors Published by the International Institute for the Science of Sintering This
article is an open access article distributed under the terms and conditions of the Creative
Commons mdash Attribution 40 International license
(httpscreativecommonsorglicensesby40)
J Vujančević et alScience of Sintering 50 (2018) 39-50 ___________________________________________________________________________
49
Maldonado-Hoacutedar Appl Catal B Environ 217 (2017) 540-550
3 H Zhang X Chen Z Li J Kou T Yu and Z Zou J Phys D Appl Phys 40 21
(2007) 6846-6849
4 M Sabarinathan S Harish J Archana M Navaneethan H Ikeda and Y
Hayakawa RSC Adv 7 40 (2017) 24754-24763
5 M R Hoffmann S T Martin W Choi and D W Bahnemann Chem Rev 95 1
(1995) 69-96
6 K Nakata and A Fujishima J Photochem Photobiol C Photochem Rev 13 3
(2012) 169-189
7 D Fang Z Luo K Huang and D C Lagoudas Appl Surf Sci 257 15 (2011)
6451-6461
8 J M Macak M Zlamal J Krysa and P Schmuki Small 3 2 (2007) 300-304
9 Y Lai L Sun Y Chen H Zhuang C Lin and J W Chin J Electrochem Soc
153 7 (2006) D123
10 Y Sun K Yan G Wang W Guo and T Ma J Phys Chem C 115 26 (2011)
12844-12849
11 H J Oh J H Lee Y J Kim S J Suh J H Lee and C S Chi Appl Catal B
Environ 84 1ndash2 (2008) 142-147
12 N Masahashi Y Mizukoshi S Semboshi and N Ohtsu Appl Catal B Environ
901ndash2 (2009) 255-261
13 J Zhang Q Xu Z Feng M Li and C Li Angew Chemie Int Ed 47 9 (2008)
1766-1769
14 J Yu and B Wang Appl Catal B Environ 94 3ndash4 (2010) 295-302
15 O Carp C L Huisman and A Reller Prog Solid State Chem 32 1ndash2 (2004) 33-
177
16 B D Cullity Elements of x-ray diffraction Reading MA Addison-Wesley
Publishing Company Inc 1978
17 A G Kontos et al Chem Phys Lett 490 1ndash3 (2010) 58-62
18 Z Su and W Zhou J Mater Chem 21 25 (2011) 8955
19 G K Mor O K Varghese M Paulose K Shankar and C a Grimes Sol Energy
Mater Sol Cells 90 14 (2006) 2011-2075
20 Y Li et al Appl Surf Sci 297 (2014) 103-108
21 T Ohsaka F Izumi and Y Fujiki J Raman Spectrosc 7 6 (1978) 321-324
22 W F Zhang Y L He M S Zhang Z Yin and Q Chen J Phys D Appl Phys
33 8 (2000) 912-916
23 H C Choi Y M Jung and S Bin Kim Vib Spectrosc 37 1 (2005) 33-38
24 Y Hara and M Nicol Phys Status Solidi 94 1 (1979) 317-322
25 B Santara P K Giri K Imakita and M Fujii J Phys D Appl Phys47 21 (2014)
215302
26 Z Lou Y Li H Song Z Ye and L Zhu RSC Adv 6 51 (2016) 45343-45348
27 X Zhu J Chen X Yu X Zhu X Gao and K Cen RSC Adv 5 39 (2015) 30416-
30424
28 Y Fu H Du S Zhang and W Huang Mater Sci Eng A 403 1ndash2 (2005) 25-31
29 Z Fan H Guo K Fang and Y Sun RSC Adv 5 31 (2015) 24795-24802
30 Y K Kho A Iwase W Y Teoh L Madler A Kudo and R Amal J Phys Chem
C 114 6 (2010) 2821-2829
Садржај Једнодимензионе наноцеви TiO2 усправно орјентисане на супстрат добијене
су електрохемијском анодизацијом титанијумске фолије у киселом електролиту У
циљу промене кристалне структуре и морфологије филма анодизовани аморфни
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
50
филмови TiO2 синтеровани су на високој температури Морфолошка промена
посматрана је скенирајућом електронском микроскопијом (СЕМ) док је кристална
структура испитивана рендгенском анализом (ХРД) и Раманском спектроскопијом
Хемијски састав је урађен помоћу спектроскопске фотоемисије X-зрака (ХПС) У овом
раду је испитиван утицај кристалне структуре и морфологије нанотубуларног филма
TiO2 на фотокаталитичку деградацију воденог раствора метил оранжа (МО) под
дејством ултраљубичастог зрачења Наноцеви TiO2 синтероване на 650 degC 30 мин
показују најбољу кристалоичност и фотокаталитичку активност у поређењу са
осталим филмовима TiO2
Кључне речи Титанијум диоксид анодизација синтеровање кристална фаза
фотокатализа
copy 2016 Authors Published by the International Institute for the Science of Sintering This
article is an open access article distributed under the terms and conditions of the Creative
Commons mdash Attribution 40 International license
(httpscreativecommonsorglicensesby40)
J Vujančević et al Science of Sintering 50 (2018) 39-50
___________________________________________________________________________
50
филмови TiO2 синтеровани су на високој температури Морфолошка промена
посматрана је скенирајућом електронском микроскопијом (СЕМ) док је кристална
структура испитивана рендгенском анализом (ХРД) и Раманском спектроскопијом
Хемијски састав је урађен помоћу спектроскопске фотоемисије X-зрака (ХПС) У овом
раду је испитиван утицај кристалне структуре и морфологије нанотубуларног филма
TiO2 на фотокаталитичку деградацију воденог раствора метил оранжа (МО) под
дејством ултраљубичастог зрачења Наноцеви TiO2 синтероване на 650 degC 30 мин
показују најбољу кристалоичност и фотокаталитичку активност у поређењу са
осталим филмовима TiO2
Кључне речи Титанијум диоксид анодизација синтеровање кристална фаза
фотокатализа
copy 2016 Authors Published by the International Institute for the Science of Sintering This
article is an open access article distributed under the terms and conditions of the Creative
Commons mdash Attribution 40 International license
(httpscreativecommonsorglicensesby40)